According to iPhone Dev-Team member MuscleNerd, there is a “very promising” iPhone 4S unlock in the works. This would allow users of the AT&T iPhone 4S to switch to T-Mobile, or any other GSM carrier. Please take note that the unlock will not work on Verizon’s CDMA phone, though.
The curious thing with MuscleNerd’s potential unlock is that it will not work on the iPhone 4, but only the 4S.
While this is great news, try to remember that an unlock is impossible without first having a jailbreak — which, conveniently is also rumored to be arriving soon.