It looks you won't need to wait for the official T-Mobile iPhone 5 rollout to try out T-Mobile 4G LTE on an iPhone, after all — an AT&T iPhone will get the job done just fine.
A new jailbreak tweak allows users to load a customer carrier file onto their iPhones and jump onto T-Mobile's 4G LTE network. There's a couple of catches, though. Okay, more than a couple.
First, the tweak only works for unlocked AT&T iPhones with an A1428 model number, or a factory-unlocked iPhone with a model number of A1428. Additionally, the tweak will not work on a Verizon iPhone 5, since its radio doesn't operate on AWS bands. In fact, the jailbreak tweak only activates T-Mobile LTE AWS support, so it won't do anything to help you access HSPA+ 42Mpbs on the 1700 MHz frequency. You can either have 4G LTE with the tweak or HSPA without it.
It's probably also worth pointing out that T-Mobile's LTE network has only launched in seven markets so far: Baltimore, Houston, Kansas City, Las Vegas, Phoenix, San Jose and Washington D.C. If you don't live near one of these areas, this tweak will do nothing for you. iTech Post is based in New York so we can't vouch for the tweak, either, but SlashGear seems to think it's legit.
For those of you brave enough to try the new tweak yourselves, we've reposted the step-by-step instructions below, courtesy of Leimobile.
START HERE:
So you purchased an unlocked iPhone 5 before T-Mobile released their new version of the iPhone 5 that supports 1700mhz. This could be the AT&T model or the officially unlocked version sold by Apple. Please understand that if you have a Verizon iPhone 5 you will not be able to connect to T-Mobile's LTE network. It does not have the correct LTE band. Currently T-Mobile only has a few cities listed that have support for LTE and they are upgrading towers all year long.
Now that you have an unlocked AT&T model A1428 or an officially unlocked model A1428 you can proceed to follow the instructions below to load a custom carrier file onto your iPhone and enable LTE. This will only work on A1428 model iPhone 5′s.
This is the guide to enabling LTE on your iPhone 5 model A1428 for T-Mobile.
1. Open Cydia
2. Tap "Manage" and then tap "Sources"
3. Tap "Edit" then tap "Add" and put the following URL into the text box: https://v.backspace.jp/repo
4. Once the URL is entered in tap "Add Source" and allow for it to download all of the repo's info and packages.
5. After your iPhone has refreshed, tap the v.backspace.jp/repo field or go to the search bar and find the package CommCenter* patch...
6. Once you have found it, install it and then reboot your iPhone once completed.
7. After the iPhone has restarted, open Cydia once again.
8. Search for iFile. The free version includes basic features. You will want to purchase it to take advantage of all of the features.
9. Once you have found it, install it. No reboot is required, though you can do it just to be on the safe side.
10. Once iFile has been installed, close Cydia and click on this file from your iPhone and click "Open in iFile"
11. Once you're in iFile tap "Unarchiver" and 3 files will show up above T-Mobile LTE.zip
12. At the top, tap "edit"and tap the dots with a check mark next to carrier.plist, carrier.pri, overrides_N41_N42.plist, and overrides_N41_N42.pri
13. Tap the clipboard icon at the bottom and tap "cut"
14. Now tap "done" at the top and tap the house icon at the bottom then tap Library, then tap Carrier Bundle.bundle (the one in blue), and then tap edit at the top again and tap the clipboard icon. Tap "paste" and it will auto inject the carrier files into the carrier folder overwriting the other files. (you may want to make a backup of these files in case anything goes wrong or we have a backup below.)
15. After the files have been placed, exit iFile and restart iPhone. After the iPhone restarts, allow it to acquire signal and display the T-Mobile logo then go to where you edit the APN settings (Settings ->General->Cellular) click reset network settings. Once that is done, enable the LTE toggle and you're good to go. The APN to connect to T-Mobile LTE is fast.t-mobile.com and the apn for Internet Tethering on T-Mobile is pcweb.tmobile.com
