Word on the street is that an update will be hitting the iPhone 5 on April 5th that will turn on access to T-Mobile's LTE network on unlocked GSM models. While you'll have to wait until April 12th to pick up the iOS handset direct from the magenta-hued carrier, those who have been running rogue with unlocked devices from AT&T or purchased direct from Apple should soon be able to run at full, blistering 4G speeds. (Where the fledgling network has been fired up, at least.) The internal notice obtained by TmoNews (which you can see after the break) reads:

"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."

So it's not just LTE, but also some of the basic features that make the iPhone such a compelling product, which will suddenly turn on for T-Mo customers. We'll know soon enough if there's truth to these rumblings, but we'd imagine the iOS update would need to be pushed out ahead of the official T-Mobile iPhone launch.