According to the FCC ID: T-mobile 9100 and suppposed to be AT&T's 9110 version. Based on the RF reports the phone carries its 3G on WCDMA Bands I, II, and V, which means it will work on AT&T (and Rogers, Bell, and Telus for the Canadians in the room) and most Europe.
Hopefully it wont have the same 3G issues it has on the T-Mobile network.
With T-Mobile already carrying the phone, Verizon soon getting the phone, and AT&T soon bringing this to it's network it seems Sprint is falling behind and counting their pennies on the "Supersonic."