BGR has gotten its hands on photos of a white iPhone 4 prototype with T-Mobile USA 3G Bands. The internal model is N94 (Verizon was N92, GSM was N90) and it runs an internal build of iOS 4. The internal build includes Apple test apps such as Radar and the employee directory app. The front of the iPhone has a different proximity sensor from the recently surfaced white iPhone.
Although it does not make sense to release a white iPhone 4 with T-Mobile at this time, Apple could still be testing the T-Mobile friendly radio with the current iPhone hardware. Maybe T-Mobile USA will finally offer the iPhone with the launch of the iPhone 5. If not, if the AT&T and T-Mobile acquisition gets approved, eventually the iPhone will make its way to to T-Mobile.