And, more tellingly in combination with this, the Iphone is still AT&T exclusive in the U.S., even though making a T-Mobile version would be essentially trivial

And, more tellingly in combination with this, the Iphone is still AT&T exclusive in the U.S., even though making a T-Mobile version would be essentially trivial (different UMTS band) and Apple already has a history of larger radio hardware customizations for carriers (no wifi in mainland China).