MiTime was just released by PushFix folks to activate FaceTime on iPhone 4. This app does not come for free, and will allow iPhone 4 users on unofficial carriers to activate FaceTime on their phone.
It costs $6 at the moment. After purchase, you will have to follow some instructions to activate it.
MiTime for iPhone 4 has been released for all the users on unofficial carriers using iPhone 4. This product allows you to activate FaceTime on phones that are operating on unofficial carriers.
This app uses just two SMS messages from your iPhone 4 and will work worldwide. You should be able to receive international text messages in order for this to work.