T-Mobile's iPhone Is Unique Variant of AT&T's Model
T-Mobile's version of the iPhone 5 has the same model number (A1428) as the one sold by AT&T, yet has unique tweaks that make it compatible with T-Mobile's WCDMA/HSPA+ network in the 1700 MHz AWS band. Unlocked A1428 iPhone 5s sold by AT&T and Apple will be able to work with T-Mobile's LTE 1700 and WCDMA/HSPA+ 1900 networks with a minor software update, but will never work with T-Mobile's WCDMA/HSPA+ 1700 network, according to an Apple product manager at today's T-Mobile event. That means only iPhone 5s sold by T-Mobile will have full high-speed data coverage from day one. Unlocked iPhone 5s used with T-Mobile will have limited high-speed data coverage at first, improving as T-Mobile makes progress with its network modernization this year.
from Phone Scoop
NOT quite Unique!
http://www.anandtech.com/show/6860/apple-to-ship-upd ... »
But yes, you must buy a new t-mobile iphone 5 to get the AWS HSPA+ support. I'd bet at&t pushed against a firmware update on existing iphones.
Not exactly accurate
The A1428 iPhone 5 variant has always possessed the physical capability for W-CDMA 2100+1700 (i.e. AWS). However, Apple implemented a software lock out to appease AT&T. The software lock out is being...
Will wifi calling be available?