A new hack allows a current-generation AT&T iPhone 5 to operate on the 1700MHz band of T-Mobile's network, reports claim. The method
involves a custom carrier file, and demands an unlocked A1428 model of the phone, whether with AT&T or officially unlocked by Apple. Once active the hack only provides access to LTE, and not T-Mobile's HSPA+ network.
Full support of T-Mobile will require the new iPhone model
Apple is preparing for April 12th. The device will still carry the A1428 designation, but feature slightly revised hardware. After it debuts the revision will become the standard GSM iPhone for both AT&T and T-Mobile customers, allowing people to switch between the two carriers. Sprint and Verizon will continue to require carrier-specific phones.