Pretty sure T-Mobile's 3G HSPA+ network runs on spectrum frequencies that are incompatible with AT&T iPhone. Definitely not the same as AT&T's. For example, the

Pretty sure T-Mobile's 3G HSPA+ network runs on spectrum frequencies that are incompatible with AT&T iPhone. Definitely not the same as AT&T's. For example, the GSM-based Nexus S sold in the US works as a voice phone on AT&T or T-Mobile but can only do 3G data on T-Mobile.