T-Mobile has yet to receive Apple’s (AAPL) blessing to become an official carrier of the iPhone. Regardless, the nation’s fourth largest carrier is encouraging customers to purchase an unlocked GSM iPhone¬†from Apple that can be used on its HSPA+ network. The recently announced iPhone 5 uses a new nano-SIM card, however, unlike the iPhone 4S which used a micro-SIM. An alleged internal document published by TmoNews on Friday confirmed earlier reports stating that T-Mobile will be offering nano-SIM cards for unlocked iPhones in October. The iPhone 5 is available in 16GB, 32GB and 64GB models in both white and black, an unlocked devices will cost $649, $749 and $849 respectively.