T-Mobile will begin carrying nano-SIMs in mid-October according to a tweet from the carrier's support account and confirmation from a T-Mobile spokesperson. We've already noted T-Mobile's desire to attract customers by providing SIM cards for customers who wish to use unlocked devices, namely iPhones, on its network, so this announcement was entirely expected. However, for those interested in using an unlocked iPhone 5 on T-Mobile's network, note that the carrier's 3G service is not supported by the iPhone, so most users will be limited to 2G EDGE service. In order to remedy this problem, T-Mobile has iPhone-compatible 4G HSPA+ currently operational in Seattle, Las Vegas, and New York City, and the carrier says that it will be available in more markets by the end of this year.
@ceciltavares We will be looking at getting them mid October :) ^LS— T-Mobile USA (@TMobileHelp) September 12, 2012