having worked as a Cs rep for AT&T wirless, i can give you some info. first off...t-mobiles coverage is horrible. if you look at their coverage map and compare it with Cing/att you'll see what i'm talking about. secondly if your going from sprint(CDMA) to tmobile, cing, att (GSM) you'll want to get a phone that does all the freq's in the US, there are some phones that only do 1 (900 or 1800 not sure can't remember) but you want to be sure that the phone does both, especially 850 mhz, that'll give you advanced signal strength and less dropped calls. Don't go into a cingular store asking for a "tri-mode" phone, cing, att and tmob don't use those kinds of phones, just ask them for a phone that does the 2 freq here in the US, once they show you those phones, pick one of those. if you need some model numbers let me know and i'll give you some you can ask to look at.