TmoNews has reportedly gotten their hands on an internal document that reveals T-mobile’s plans to enable 4G LTE, visual voicemail, MMS settings, and more for unlocked iPhones via a carrier software update on April 5, 2013:
The T-Mobile Carrier Update is a minor iOS software update that enables official iPhone support by T-Mobile. When installed, the software update enables a handful of capabilities like Visual Voicemail, MMS Settings and Network/Device optimizations that customers do not have access to today. On April 5, the software update will begin being pushed via OTA to all iPhone devices on the T-Mobile network with iOS 6.1.x or higher.
T-mobile will also be offering HD voice, a feature of the iPhone 5 that has yet to be taken advantage of by the top U.S. cellular carriers. AT&T announced last night that the feature will be coming to AT&T customers later this year; however, T-mobile says the feature will be supported on their iPhone 5 right out of the box.
Sources: TmoNews via MacRumors