I do not understand why anyone cares what carrier it is released on. Android phones can be unlocked and rooted to work on any carrier. If i can use an Evo or a Droid X on services like cricket or metropcs then im sure you can find a way to move it off t-mobil
Clearly you're forgetting that CDMA and GSM are not compatible. So I can't use a Verizon DROID on AT&T. Not to mention, why would I buy a T-Mobile phone to use on AT&T when I'd be on EDGE all the time, instead of 3G.