this is where i put the funny searchbutton.gif i am too lazy to find
this has been discussed over and over again. t-mobiles 3G network in the US uses the 1700 band. so if the 3G iphone does not support the 1700 band (which is not likely), then the 3G portion of the phone will not function on t-mobiles network. you could still use the phone to make calls, just not on t-mobiles 3G network for data.