Introduction

The story of the Verizon iPhone 4 is definitely an astonishing one. Leading up to nearly every iPhone release was endless speculation that a CDMA version would launch simultaneously, finally bound for the largest carrier in the US. The combination of carrier exclusivity, endless reports of AT&T's 3G failing during trade shows and conferences, pent up demand, and numerous other factors combined to create a perfect storm of rumor and mystery. Each time, analysts, insiders, and pundits alike were certain it was just months away - and then prove to be no more well informed than the rest of us.

It's surreal to think that everyone finally got it right. In retrospect, it also seems fittingly ironic that Duke Nukem Forever will launch the same calendar year as the Verizon iPhone 4.

The truth is that what differs between the Verizon iPhone 4 and its older brother isn't a whole lot - and that's overwhelmingly a good thing. In case you're just starting out, the main difference between the two is entirely network technology. In the USA, carriers such as Sprint, Verizon, US Cellular, MetroPCS and a number of others use 3GPP2 camp technologies for a variety of reasons. These are CDMA2000-1x, and CDMA2000-EV-DO, known colloquially as just 1x and EVDO.

The story goes something like this. Europe and the majority of the planet soon after adapted GSM for 2G, then 3GPP technologies for 3G - UMTS, HSPA, and now LTE all are under the 3GPP umbrella. In the USA, AT&T and T-Mobile are the dominant carriers running network tech from the 3GPP camp. Both have GSM/EDGE 2G and UMTS 3G networks.

The confusing bit in here is that CDMA is often confused with CDMA2000. On its own, CDMA refers just to the multiplexing scheme used - Code Division Multiple Access. Both CDMA2000 and UMTS use CDMA as the multi-user access scheme, the difference is primarily that UMTS allows 5 MHz channels (WCDMA) whereas CDMA2000 uses 1.25 MHz channels for data and voice. Before UMTS arrived on the scene, the distinction made a bit more sense since GSM is TDMA - Time Division Multiple Access.

Apple shopped around for a carrier to bring its iPhone to, and settled on Cingular after getting the door slammed in its face by everyone else, or so the legend goes. Cingular became AT&T, Apple released a GSM/EDGE 2G phone, then three 3G phones with different levels of HSPA support, and you know the rest.

Physical Differences

It's boring to start out a review with a history lesson though, so let's stop there. On to what's different about the CDMA version of the iPhone 4. 

The Verizon iPhone 4 has a noticeably different outside appearance. The AT&T (GSM/UMTS) iPhone 4 is on top, the Verizon (CDMA) iPhone 4 is on the bottom in all the following photos.

The black stainless steel strip at the top has moved to the far left side, displacing the vibration switch by a mm or two. 

The right side has a new symmetrically placed black strip as well. The two at the bottom remain the same on both sides. Obviously the other big change is the absence of a SIM slot entirely - oh and likewise there's no SIM ejector tool in the box.

On the back, there's another more aesthetic difference. The Verizon iPhone 4 lacks the regulatory labels that adorn the AT&T version. Gone are the FCC, non-recyclable battery, and European Conformity CE markings. Apple seems to do something to visually distinguish each iPhone based entirely on the back. The iPhone 3GS brought chrome on the back to distinguish it from the 3G, and the CDMA iPhone 4 does away with some iconography. Fair enough.

On the bottom nothing much is changed, though the Verizon iPhone 4 comes with pentalobe screws whereas our launch iPhone 4 has phillips.

One of the other interesting changes is how vastly different the vibration unit is. I was a bit skeptical that the difference would be perceptible - it's actually noticeably different. The older vibrate unit feels loud and harsh, like something inside is actually rattling around. Of course, the old vibration unit is rather standard fare for phones - a counterweight on a motor. The new vibration unit occupies much more area inside, but the vibration feel is entirely different. It's almost completely silent, and makes the entire phone feel like it's moving as one complete piece. It's difficult to describe - it's a deeper and more precise vibration.

I've put together a video overview of everything there is to mention about the Verizon iPhone 4, and included in there is a demonstration of how silent the new vibration unit is. 

Not making any noise while vibrating is both a good and bad thing depending on the context. I always leave phones on vibrate, so having them make some noise is occasionally useful. It's virtually undetectable now, so if you leave the phone on a desk and have a call come in, chances are good you'll miss it unless you can feel the vibe.

On the flipside, it's a completely different experience when you're on a call and an email or SMS comes in. This is when not having the vibrate unit not make any noise is a godsend. Previously, the vibration was intense and noisy enough to make it difficult to hear the other party, and at the same time the noise was audible on the other side of the call. Now, it's silent enough to not interrupt the conversation or cause a lapse in audibility at all.

A CDMA Baseband

The majority of the CDMA iPhone story is one of network-related changes, and first up is an entirely different baseband. The UMTS iPhone 4 uses the Infineon X-Gold 618 baseband, which supports HSDPA 7.2 Mbps and HSUPA 2.9 Mbps. By contrast, the CDMA iPhone uses the Qualcomm MDM6600, which is a dual-mode GSM/UMTS and CDMA2000-1xRTT/EVDO part capable of even doing HSDPA 14.4 on the downlink. The Verizon iPhone tunes 800/1900 MHz CDMA2000-1xEVDO Rev.A for peak throughput of 3.1 Mbps down, 1.8 Mbps up. The MDM6600 supports Rev.B speeds, but it's unlikely we'll see carriers pursue 3GPP2 tech any longer, besides a possible 1xAdvanced rollout.

CDMA iPhone 4 - Network Support
CDMA2000-1xEV-DO	800 / 1900 MHz
Speed (Downstream/Upstream)	3.1 Mbps / 1.8 Mbps
Baseband Hardware	Qualcomm MDM6600

Though the baseband supports dual mode operation, upon looking at more of the CDMA iPhone disassembled, it's quickly apparent why that isn't put into use. There simply isn't space for the required power amps as the mainboard is organized right now. Though there's definitely space picked up from losing the SIM slot (which, as an aside, explains why Apple seemed keen on losing SIMs entirely - it's starting to become a huge chunk of real-estate), but the MDM6600 is simply larger than the Infineon X-Gold 618. Unless you can get in there and add both the signaling for the SIM and necessary RF components, there's no way the CDMA iPhone is becoming dual-mode anytime soon.

Qualcomm MDM6600 from iFixit

The MDM6600 also has A-GPS (GPSone) support onboard, which the CDMA iPhone uses. There's no longer a dedicated Broadcom part doing GPS heavy lifting, it's just all onboard the MDM6600. Interestingly enough, the MDM6600 also has Glonass support, though I doubt it's being used. The MDM6600 also has a dedicated I2C interface for NFC, but you still need a third-party radio and controller solution.

Signal Attenuation

Last time we visited the iPhone 4, a large part of our focus centered on getting to the bottom of the signal attenuation issue. With the UMTS iPhone 4, if you touched the exposed stainless steel band in the wrong place, the antenna would capacitively de-tune, signal strength and quality would both fade, calls and data sessions could potentially drop, and all hell broke loose accordingly.

Most of the antenna problem is actually mitigated in the CDMA iPhone 4. How? Antenna diversity.

Antenna diversity can be implemented a few different ways. You can switch between two different antennas quickly depending on which is experiencing temporary fade (from a hand touching it), or you can do some averaging and hope that even with significant fade on one antenna, there's still enough signal to keep you above cutoff. It's not clear what Apple has implemented on the CDMA iPhone 4, but as we'll show later, it definitely mitigates the problem in most cases. Diversity won't magically give you better signal strength (nor will it save you if you cover both), but it will help keep SNR and overall link quality high. The MDM6600 has full CDMA and WCDMA RF receive diversity support with the inclusion of an external switch. It's not entirely certain what part is the switch, but it's definitely there.

How else do we know that the CDMA iPhone 4 has diversity? It's part of Verizon's own specifications for what devices need to have to attach to their network. Buried in the required open alliance spec datasheets is the following:

There we have it, if you want a device approved for Verizon's EVDO network, you need receive diversity.

Inside, the CDMA iPhone has a substantially changed antenna and RF design to accommodate that diversity. There are two cellular antennas in the CDMA version, as opposed to one in the UMTS version. With the phone facing up, the first cellular antenna consists of the new strip at the very top. The second is the strip running from the bottom left, across the bottom, and up the right side of the phone. The far left side with volume buttons and the vibrate switch is part of the WiFi and Bluetooth antenna.

Inspecting the RF path itself, we can see that the bottom acoustic module and cellular feed line is relatively unchanged. It snakes across from the region near the baseband to the attach point right next to the black strip. This connector across the base isn't an antenna, just a feed line. This is the sole cellular antenna in the UMTS iPhone 4, and is essentially unchanged. We didn't take apart an iPhone, these are just photos from the FCC.

What is changed is the new second cellular antenna. There's another cable which runs on the underside from near the baseband, straight up the length of the entire main PCB. It snakes around a screw, continues up, and then attaches to another UFL connector at the top. The trace is easily followed up to a gold contact point which presses against a mating point on the top strip. This is the second cellular antenna.

The other interesting aspect is the WiFi/BT 2.4 GHz antenna. Broadcom is still in the CDMA iPhone doing the heavy lifting for 802.11b/g/n and Bluetooth. There's another connector right next to the BT/WiFi module which leads to a cable that flexes around, then connects to the final strip.

There's a beefy flex region which could be a ground plane, and then the screw connector for that last strip.

So there's a lot that's been changed between the UMTS and CDMA iPhone 4 internally - how much of a difference does it actually make in practice? It's actually pretty substantial.

When Anand got time with the CDMA iPhone 4 at the announce event, he snapped a number of photos of field test which at the time worked perfectly. Back then, the CDMA iPhone 4 was running iOS 4.2.5, and there were fields like these visible:

Look at Rx AGC0 and AGC1, and the accompanying signal fields. There's Rx diversity again, by the way. 

I was definitely excited to see that things were going to be relatively open once more, which would make it easy to fully appreciate the design changes and just how much better everything is. Right before launch however, Apple pushed iOS 4.2.6 live which did more than just ensure the hotspot feature reports data correctly - it removed field test. Yeah, we're right back to how things were when iOS 4.0 launched and everything was wrapped in enigma.

It's a shame that field test is gone because it looked very comprehensive. I hope it mysteriously reappears randomly just like it did in iOS 4.2. Its absence right now isn't a big deal though, because we can still get numerical values by doing the same thing we did last time we were in this situation. There's no jailbreaking involved, either. It still works, and we can still read numerical values (in dBm) out. 

 
Note "3G" for EVDO data, "o" for 1xRTT which was previously reserved for GPRS

From playing around it's obvious that the measurement corresponds to 3G EVDO and not 1xRTT. Historically all phones on Verizon used to show EVDO and 1x signal side by side, which is honestly the right way of doing things - they're different channels, often on different bands, with different tolerances. Having good 3G EVDO signal doesn't imply good calling area at all, but Android makes the same mistake, and we can only really fight so many battles.

Another interesting bit is that the signal status icon shows 3G for EVDO, and the circle once reserved for GPRS for 1xRTT data. That's a bit harsh considering how glacially slow GPRS is, 1xRTT is more comparable to EDGE, but I guess having consistent iconography does make sense.

Signal Attenuation Comparison in dB - Lower is Better
Device	Cupping Tightly	Holding Naturally	Holding in Case	On an Open Palm
Verizon iPhone 4	16.5	15.5	9.0	7.9
AT&T iPhone 4	24.6	19.8	7.2	9.2
LG Optimus 2X	13.7	9.3	-	5.9
Nexus S	13.3	6.1	-	4.3
Droid 2	11.5	5.1	-	4.5
BlackBerry Torch	15.9	7.1	-	3.7
Dell Streak	14.0	8.7	-	4.0
Droid X	15.0	5.1	-	4.5
iPhone 3GS	14.3	1.9	3.2	0.2
HTC Nexus One	17.7	10.7	7.7	6.7

Held very tightly in true death-grip fashion, the signal drop is around 16 dB, which is right in the neighborhood of every other smartphone we've tested. Hold a little lighter, and it drops down to around 15 dB. Toss a case on there, and obviously attenuation is way lower at around 9 dB. Death grip is essentially mitigated, and the attenuation when held is now comparable to other smartphones. What we're measuring, of course, is just the numerical signal strength being reported.

There's still a way to make signal drop dramatically - cover both antennas. I call this move the double-fist, since it literally requires you to cup both the top and bottom of the phone like some sort of deranged squirrel. You could try and argue that this is still sort of like deathgrip, but it's in no way a natural way of holding the phone, ever. To be thorough, I tested this position and found that I could cause a drop of around 21 dB doing my absolute best to cover the top, bottom, and side with my hands. This is the absolute worst case possible, and if you're seriously using two hands, you're purposefully inducing attenuation. Even with it gripped like this, I have yet to make any calls or data sessions stop.

Death grip is essentially mitigated. I feel completely confident using the CDMA iPhone 4 without a case, and did so for the duration of all this testing without once dropping off the network. Getting a case still makes sense, but using the phone without one is no longer something that will dramatically affect phone usability.

WiFi

Of course, the WiFi antenna is tweaked slightly as well, though both iPhone 4 versions use the same 802.11b/g/n and Bluetooth stack. I spent a lot of time comparing performance around the house and found that the difference between the two is nearly indistinguishable.

After letting both indicators settle, the reported WiFi RSSI on the CDMA iPhone was always within 3 dB of the GSM/UMTS iPhone 4. In the photos above, that's the set of numbers after the carrier string (-76 on both of these). Wireless range before falling off  the network was nearly identical as well, as expected. It's obvious to me that a lot was done to keep things comparable. They both use the strip with the volume buttons and vibrate switch.

GPS

GPS is no longer being handled by a discrete single-chip solution from Broadcom (the GSM/UMTS iPhone used a BCM4750 for A-GPS). Instead, the CDMA iPhone 4 uses the integrated A-GPS on the Qualcomm MDM6600.

I set out to find whether performance was any different, and discovered that the CDMA iPhone has slightly better GPS accuracy and tracking. The difference isn't substantial, but the CDMA iPhone 4 routinely presents a smaller blue circle and better reflects actual position when given the same swath of open sky as the GSM/UMTS iPhone 4. Fix times between the two are equally speedy and indistinguishable.

I put both phones face-up on my dashboard and went driving around for a considerable time, long enough to let both get good quality 3D GPS fixes. Surprisingly enough, the CDMA iPhone had much better precision and accuracy, and consistently better tracking compared to the GSM/UMTS version. I recorded a short video showing the differences, please excuse the vibration.

From an RF perspective, it's hard to argue that the CDMA iPhone isn't superior. Moreover, it'd be nice to see the next GSM/UMTS iPhone also reflect some of the numerous improvements in the CDMA version, including receive diversity and better GPS.

Simultaneous Calls, Texts, Data

So if you've heard anything about the Verizon iPhone 4 versus the AT&T iPhone 4, you've heard about simultaneous voice and data. Truth is that on UMTS voice and data are multiplexed, and you can do them at the same time. On 1xEVDO you can either transact voice, or data, but not both at the same time. If you try to do it on the Verizon iPhone 4, you get a screen like this:

It isn't really just voice that interrupts data, however. Text messaging (SMS) does it as well. If you're surfing along and an SMS comes in, data pauses for about three or so seconds while the phone goes down to 1x, gets the SMS, then reacquires EVDO. A lot of people don't know that SMS is still over voice on the CDMA camp. If you're doing lots of texting and surfing at the same time, this can get annoying fast. If you're being bombarded with lots and lots of SMSes, you can't transact any data until all of them are done showing up. You can see behavior for yourself in our overview video as well. 

There's also another set of nuances between the CDMA iPhone 4 and UMTS iPhone 4. Conference call features are different, and there are a lot of small things. Whereas the UMTS iPhone 4 can support up to five simultaneous lines, the CDMA version only supports two.

There were also toggles for call forwarding, call waiting, and caller ID toggles on the UMTS version. These are notably absent on the CDMA version, instead you'll need to enter appropriate * codes for those (*72 and *73 for forwarding, *70 for call waiting, *67 for caller ID). That's not an Apple thing but rather a network limitation.

An even larger (but oft overlooked) difference are the SMS differences between the CDMA carriers and UMTS. The CDMA SMS specification has no support for messages with characters outside of ASCII. Send or receive one with "Emoji" or other non-ASCII characters from a CDMA iPhone 4, and you'll get no alert, it just disappears.

One of the huge selling points of GSM for me personally has been long SMS support. If you routinely send texts that are over 160 characters, UMTS/GSM generally wins because most carriers implement long SMS support properly. Verizon had had its own message concatenation back in the day, but I've yet to see it really used on a smartphone of theirs. It was one of the first things I tested against a friend of mine who also has a Verizon iPhone 4. Turns out that between Verizon customers, SMS concatenation does work, and long multi-texts are combined into one. That's hugely awesome if you SMS as much as I do.

However, concatenation doesn't always work between carriers. That's not a carrier specific thing, but just crappy SMS interchanges between carriers being a problem.

 

Data Speed Differences

There's a big difference in both voice quality and speed between the CDMA and UMTS networks in the US. Again, that's one of those huge loaded statements that's subject to a ton of different factors. How loaded cells are, what frequency bands carriers are licensed to use in your market, signal strength, and other factors make it impossible to say definitively which is better.

There's really no sugar coating the reputation that AT&T has gained for having issues in a number of notable metropolises, most of which the carrier claims are fixed. The bigger problem is at conferences, where 3G generally stops responding entirely - I've found myself spending the duration of most on EDGE, where things actually work. In those circumstances, the problem is one of network saturation rather than a technical difference between CDMA2000 and UMTS.

 Fastest downstream test I've gotten on the Verizon iPhone

When it comes to data, I've found that EVDO downstream speeds average between 600 and 800 kilobits/s, peaking with the occasional burst up to 2 megabits/s depending on signal quality and load. Upstream speeds sit around 600 kilobits/s with occasional bursts up to around 1 megabits/s. I ran over 230 speedtests using the speedtest.net app on the Verizon iPhone throughout my market all over town. The Verizon iPhone averaged 685 kilobits/s down, 583 kilobits/s up. I saw a maximum downstream rate of 2.24 megabits/s and maximum upstream rate of 1.03 megabits/s. Keep in mind that Verizon's EVDO Rev.A network supports 3.1 megabits/s down and 1.8 megabits/s up per 1.25 MHz channel in theory.

Device	Verizon iPhone 4	AT&T iPhone 4
Average Downstream	0.69 Mbps	2.03 Mbps
Maximum Downstream	2.24 Mbps	4.89 Mbps
Average Upstream	0.59 Mbps	1.08 Mbps
Maximum Upstream	1.03 Mbps	1.72 Mbps

I ran the same number of speedtests at the same time and place using the AT&T iPhone 4. In my market, AT&T is allegedly HSDPA 14.4, though I still don't have any devices of the appropriate UMTS class to test and find out. Remember that the iPhone 4 is still a HSPDA 7.2/HSUPA 2.9 device, so it wouldn't make a substantial difference anyhow. I saw an average downstream throughput of 2.02 megabits/s down, 1.08 megabits/s up. Maximum throughput was 4.89 megabits/s down, 1.72 megabits/s up.

I'd say that when it comes to average speed, results like these are pretty typical for comparing Verizon's EVDO Rev.A data to AT&T HSPA data. In pretty average locations (I tested throughout a mall, driving around, in residential, e.t.c.) AT&T is simply faster - there is a tradeoff however. The other consideration is how Verizon's 1xRTT data compares to GSM's GPRS and EDGE. 1xRTT links are 154 kilobits/s up and down, EDGE can be around 200 kilobits/s down, and GPRS is abysmally slow.

Subjectively, the tradeoff between AT&T and Verizon data is one between speed and coverage. While AT&T is much faster close to the cell center, at the edges throughput can suffer substantially. Anecdotally Verizon EVDO throughput seems to be much more uniform throughout the cell, even out at cell edge. Some of my fastest 2 Mbps results on the Verizon iPhone were below -80 dBm.

Personal Hotspot

A huge difference between the two iPhones is the presence of WiFi hotspot functionality. Get the appropriate $20/month add-on, and you can turn the iPhone into a wireless router without having to jailbreak and use something like MyWi.

The hotspot puts you behind a NAT, on 172.20.10.x subnet. Configuration is easy - just toggle it from under network or on the first page of settings, and it'll prompt you that it's about to enable Bluetooth or WiFi appropriately. Configuration options are scant. Encryption always is WPA-PSK, there's no WPA2 or WEP option. The hotspot SSID is also always your phone name, so expect to see lots of "Brad's iPhone" and the cliché "Titanic" AP names pop up at cafes and conferences very soon. Also, the hotspot connects clients at the standard 802.11n rate for 1 spatial stream - 72 Mbps. 

  

When the hotspot is on, you're not actually shown anything. Only when users connect does a blue strip appear just like the green call-in-progress one. Tapping on that brings you immediately into the hotspot settings page. That actually is a bit frustrating if you've got the hotspot going for a friend but want to browse on the phone and use the scroll-to-top gesture.

I've been hammering on the hotspot for a while and have yet to encounter any instability or crashing. Implementation here seems spot-on and stable. Of course, you're still subject to the same simultaneous text/voice and data constraints, but the pause is handled elegantly on clients.

One other notable thing - I'm running iOS 4.3 beta 3 on one of my AT&T iPhone 4s, and noticed that the hotspot logo appears in the place of the WiFi symbol when connected to the Verizon iPhone 4 hotspot. It's the same weird chain-looking symbol. It's very strange that the device can tell it's connected to another iPhone - perhaps a future feature?

Voice Quality

The other side of things is voice quality. Unfortunately we're still working on devising some objective call quality tests. On paper, the AT&T iPhone 4 supports wideband and narrowband adaptive multirate (NB-AMR and WB-AMR) voice codecs (vocoders) on UMTS. Remember that on UMTS (3G) voice and data are multiplexed and work at the same time. There's more bandwidth on that link, and as a result UMTS has a higher bitrate voice coder than GSM. That said AMR is variable bitrate (hence the name) and changes depending on link quality. UMTS has more dynamic range compared to GSM and CDMA2000 (EVRC) voice.

On the Verizon iPhone, EVRC is used as the vocoder. That's pretty much standard fare for CDMA2000 voice. The CDMA2000 spec has a number of different of vocoders, the most popular of which are 13k (for 13 kilobits/s), EVRC (which is 8, 4, or 0.8 kilobits/s), and somewhat newer EVRC-B. Way back in the day, it used to be almost trivially easy to change vocoders on Windows Mobile devices, and 13k sounded noticeably better than EVRC, which uses more compression. I've always found EVRC to be noticeably less appealing from an audio perspective than UMTS voice (WB-AMR), but roughly comparable to GSM voice. With EVRC there are audible compression artifacts at the start and end of spoken words, and more blocking and drop-out when 1x signal fades. In comparison, UMTS voice only drops out and degrades substantially right as you're at the bleeding edge of dropping the call entirely. EVRC has less dynamic range than UMTS, so it sounds subjectively louder - the tradeoff is that you lose high and low frequencies. Listening to "ess" sounds in words while on calls is always where the difference is noticeable.

The difference in dynamic range translates to the Verizon iPhone 4 being much louder, the same effect we discussed with the original iPhone 4 between calls on GSM and UMTS.

I set out to show the difference between GSM, UMTS, and CDMA2000 voice by calling the local ASOS weather station. I put together a video with the two iPhones calling the same number and running through the weather report one complete time. Unfortunately, the video camera I have doesn't quite do justice to how audibly different the three calls are, and I lack high quality audio recording equipment. We might follow up with different audio equipment soon, however.

The bigger difference between the two is reliability. Because voice and SMS goes over 1xRTT on Verizon, usually when you can't transact data, calls still work. With the AT&T iPhone 4, when saturation on UMTS happens, you won't be able to call or transact data unless you manually toggle 2G. The result is some built-in robustness for voice on Verizon purely because of that voice/data segregation. In addition, Verizon often puts 1x voice on 800 MHz spectrum and EVDO on 1900 MHz PCS where posisble, so voice coverage tends to work even in places data doesn't necessarily.

In use, the Verizon iPhone 4 will briefly show the "o" symbol for 1xRTT data and then quickly re-acquire EVDO and show "3G." After a call you can see this behavior and the quick re-acquisition of EVDO.

It'd be pure speculation at this point to predict how well Verizon's network will cope with more and more iPhone users. That said, having the data-hungry iPhone on two major carriers definitely will help spread the load as users switch depending on which is better in their market.

CDMA vs GSM/UMTS iPhone 4 Nuances

There are a bunch of other subtle differences between the two iPhone 4 models, but they're relatively small things.

 
Accessory connection warning change - Left: AT&T iPhone 4, Right: Verizon iPhone 4

First off, the "audio interference" warning that's stuck around since the first iPhone is gone, like it should be.

Remember that 2G GSM/EDGE is TDMA - Time Division Multiple Access. In that multiplexing scheme, each phone gets assigned timeslots to transmit and receive during. When the phone is transmitting, because of the very short nature of those timeslots, instantaneous power looks like a delta function - it's a huge instantaneous pulse, even though time-average power is comparatively low. Well, the spacing of those pulses inside a multiframe is 4.62 ms, which corresponds to a very audible 217 Hz. This induces audible interference in unshielded audio systems. The solution Apple came up with was to require new approved accessory devices to shield components appropriately, and use an IC that would tell the device it was shielded. Other older devices pop up an alert about audio interference. Although 3G UMTS uses WCDMA, (which is fundamentally the same multiplexing scheme as CDMA2000, just a wider channel) the alert pops up regardless of whether the AT&T iPhone is on 2G or 3G. The phone can transmit continuously (no short, bursty nature) across the entire channel, and interference doesn't occur.

If you connect up a GSM iPhone to something that isn't shielded, you used to get that above dialog regardless of whether you're on 2G or 3G. Apple removed the audio interference part of that message, instead only warning about some attenuation which might happen from using a dock or battery.

There aren't too many other notable things - it's the same app store and interface as the AT&T version. There's no Verizon branded anything outside the carrier string. Of course, the fact that it's the same market means you can grab some AT&T specific apps like mark the spot and file some disingenuous bad signal reports. Maybe a tiny bit of app-segregation (or an API for determining whether the iPhone is CDMA or GSM/UMTS) could in fact be useful.

I noticed that the Verizon iPhone 4 also seems to get warmer than I remember the AT&T iPhone getting. It's something that's pronounced while charging or using 3G data a lot - perhaps the MDM6600 simply gets warmer than Infineon's X-Gold 618.

Screen slightly warmer

Our Verizon iPhone 4 review unit also has a noticeably warmer screen than the other AT&T iPhone 4s I've seen. Side by side with one, the difference is clearly visible. Our photos don't really do it justice, but the GSM/UMTS iPhone 4 is much more bluish than the Verizon iPhone 4, which has a warmer red hue.

I whipped out the X-Rite i1D2 used for display calibration and measured the white point. Sure enough, the Verizon iPhone 4 has a much different white point temperature than the AT&T iPhone 4. Brightness and black are similar enough to not be a huge difference, but that white point is seriously noticeable. Whereas the old iPhone 4 was reasonably close to 6500K, the panel in our Verizon iPhone 4 review unit is at 7120K. It doesn't show up in these photos or the overview video, but the difference is there.

Brightness and contrast are changed, but only slightly. 

It's not clear whether Apple changed parts suppliers or this is simply a different batch of dissimilar panels. Either way, it's enough of a difference to be apparent almost immediately. The state of color accuracy on smartphones is awful to begin with, this is just another example of how huge the variance is even across a mature product line.

The Universal Bumper

To accommodate the moved insulate black strip, Apple also had to move the vibrate switch. It's slightly lower on the Verizon model, since leaving it in the exact same place as the AT&T version would've no doubt been too close to the end of the strip to be machinable.

The result is that new bumpers and cases are required. Apple sent a universal bumper, which has a longer vibrate port cut in the side to accommodate both versions of the iPhone 4. On both, you get a gap between the end of the vibrate switch and the port, but the result is that there's one bumper SKU.

Top - Verizon iPhone 4, Bottom - AT&T iPhone 4 (in universal bumper)

Other legacy iPhone 4 cases are perfectly fine. For example, I use an Otterbox commuter which always had an oversized vibrate port. Luckily, it's just large enough to accommodate the Verizon iPhone. The position and feel of the volume up/down buttons is unchanged.

Battery Life

With a new baseband comes new battery life. We ran our usual suite of battery life tests on the Verizon iPhone 4. I was running the last test - WiFi battery life test - when it was time to hop on the plane for MWC. That test hopefully won't change too much, as it's the same WiFi/Bluetooth stack as the previous iPhone 4. As soon as we're back, it'll get tested and the graph will appear. One of the other things we've been working on is a WiFi hotspot battery life test. I've been gathering numbers from every phone so far with official support for WiFi tethering, the iPhone 4 on Verizon will be put to the test the same way. 

Update: We've added the WiFi web browsing battery life numbers down below, and they're class leading. WiFi tethering numbers are coming soon.

Call time is shockingly close between the two iPhone 4s. The Verizon iPhone 4 also soundly beats the AT&T iPhone 4 in the 3G web browsing and WiFi battery life department, shooting it to the top of our chart. Qualcomm's MDM6600 appears to be comparable if not better than the Infineon in the power department, though it's hard to be sure without having HSPA working for a direct comparison.

Final Thoughts

So the long-awaited Verizon iPhone 4 is finally here. It's functionally the same as the GSM/UMTS iPhone 4 on AT&T, except significantly less prone to unintended signal attenuation from being held thanks to receive diversity through two cellular antennas. Battery life is the same or better than the AT&T iPhone 4, GPS is slightly more precise, Verizon lets you turn your phone into a WiFi hotspot if you pay the fare, and SMS concatenation even works on Verizon's network. There's really nothing to complain about at all or point out as being inordinate about the CDMA iPhone - it's simply an iPhone 4 on Verizon's network.

 

At the same time, so many more questions linger. Where is the elusive White iPhone 4? What will iPhone 5 bring when it arrives presumably during the normal summer refresh cadence? Is the MDM6600 the baseband Apple will go with for the next device as well, perhaps this next time including the power amps necessary for dual-mode operation? It's impossible to say for sure what will happen, and we rarely dabble in such murky, speculative waters.

I have no doubt that tomes have been written about the differences between AT&T and Verizon already. It's a debate that has raged on like some sort of cellular analog of the 100-year-war, with each camp ideologically entrenched and beyond the point of reason. Ultimately, picking which is better is a matter of making tradeoffs. There's no simple way to answer which is the "better" carrier, as the figures of merit change from person to person. If voice calls are what's absolutely most important to you, get the Verizon iPhone. If much faster 3G data is what's most important to you, get the AT&T iPhone. If having more ubiquitous data coverage (at the expense of speed) sounds reasonable, get the Verizon iPhone. If the simultaneous voice/text and data issue is something you feel strongly about, get the AT&T version. Above all else, find out who has better coverage in the areas that actually matter to you - the workplace, at home, and along daily commute. Until carriers report coverage with actual numbers and following some standard, take coverage maps with a hearty dose of skepticism. The only way to know for certain is to either borrow a friend or his phone, or make liberal use of return policies.

Ultimately, the larger net effect of the Verizon iPhone 4 will be to increase pressure on Android. Verizon is the carrier that Google's platform has arguably enjoyed the most success with. Having an iPhone doing direct battle on the same carrier isn't so much optional for Apple anymore as it is necessity. Even if you disagree with the philosophical choices that iOS has made, you have to hand it to Apple for catalyzing changes that will force carrier competition based on the merits of their networks.