Shipments of nanoSIM cards have begun rolling out to T-Mobile stores this weekend. The nanoSIMs can be used with unlocked iPhones to access T-Mobile's HSPA+ network. T-Mobile has been working hard to convince iPhone users to switch carriers by promising bigger savings and unlimited data plans.
T-Mobile also began offering free iPhone support to its customers in June, and announced it was building a iPhone-compatible 4G network in May. Unlike the other big U.S. carriers (AT&T, Verizon and Sprint) T-Mobile does not officially carry the iPhone, however, it is estimated over one million T-Mobile subscribers use the Apple phone on T-Mobile's network.
Apple has not begun selling unlocked iPhone 5 handsets yet, but the Verizon iPhone 5 is compatible with GSM networks. It is also unknown how many T-Mobile stores are receiving nanoSIM shipments this weekend, so you may want to call ahead.