Activate FaceTime on Unlocked iPhone 4 with MiTime
The recently released application MiTime for the iPhone 4 fixes and activates FaceTime on unlocked iPhone 4s that run on T-Mobile USA or other unofficial unsupported carriers. According to the MiTime’s description, it should work with almost any carrier in the world. You should be able to receive international SMS messages to activate FaceTime via MiTime.
The application MiTime sends two international SMS messages for activation, so it can not be free. Thus, until there is no other way to activate FaceTime on unlocked iPhone 4s, this is the only way with an affordable price.
More information and tutorial is