Clearwire has been talking about deploying TDD-LTE (Time Division Duplexing, as opposed to FDD) on its 2.5 GHz spectrum for some time now, and has announced some more launch details today, including initial markets and a rough timeline. Clearwire is focusing on upgrading "hot zones" in urban markets first, which probably means its most actively used cell sites.

In its earnings report, Clearwire notes that it has already completed the first phase of its network overlay on 8,000 such "hot zone" cell sites, primarily ones where it can offload for future compatible Sprint and Cricket devices. Some 5,000 of such cell sites are in major markets which it is targeting for early 2013 launch, including New York City, San Francisco, Los Angeles, Chicago and Seattle. Clearwire is planning to launch its TDD-LTE network in 31 total markets by mid 2013, though it notes that it will name the specific other markets at a later date. 

As an addendum, Clearwire has been trialing and demonstrating 20 MHz FDD-LTE in Phoenix, AZ for a while now on its 2.5 GHz spectrum (LTE band 41). I would fully expect to see Clearwire take full advantage of band 41's size and run 20 MHz TDD-LTE here, and implement carrier aggregation with LTE-A in the future.

Source: Clearwire (1), (2)