TmoNews on Tuesday carried an image of a leaked screenshot showing a carrier update set for April 5. The update will bring features like Visual Voicemail, and MMS Settings, as well as "Network/Device optimizations that customers do not have access to today."
While unconfirmed, it is possible that these "optimizations" will give current iPhone owners on T-Mobile access to the network's LTE network. Currently, data speeds for iPhones on T-Mobile's network top out at 2G EDGE levels. The iPhone 5, when it reaches T-Mobile, will be able to take advantage of the carrier's new high-speed network.
Apple's iPhone 5 will make its official debut on T-Mobile on April 12, for $99 on the carrier's new UNCarrier payment plans. The OTA update for current T-Mobile iPhone users will go out to devices running iOS 6.1.x or higher beginning April 5.