iOS 6 now allows you to elegantly reject calls with a tool to the right of the standard slide to reply widget. You can now have your phone automatically remind you to call someone back either based on time or location. You can also reject a phone call and have your phone automatically respond with a message to the caller. 

iOS 6 also supports a do not disturb mode that you can turn on to avoid being woken up in the middle of the night by text messages, calls and push notifications. iOS 6 also exposes fine grained control over what calls/notfications to let through even in DND mode.