Correct me if I'm wrong, but T-Mobiles proposed 3G network will be on 2100 mhz and 1700 mhz while AT&T's current 3G network is 1900 mhz and 850 mhz. I wouldn't rule out the possibility of a mutliband chip there is a chance that the upcoming 3G iPhone will support the 1900, 850, and 2100 bands afterall the European 3G networks operate on the 2100mhz band.