According to T-Mobile, they are very serious about iPhone and it said they will have Nano-SIM Cards in stock ready this October. If you like T-Mobile, you can bring your unlocked iPhone 5 and sign it up with them. For full information, click the link below.

http://www.redmondpie.com/t-mobile-really-is-serious-about-the-iphone-will-have-nano-sim-cards-in-stock-for-iphone-5-in-october/