1. Turn on WiFi and make sure you're connected.
2. Go into the Market, search "APN Backup".
3. Download the program called "APNsBU (ROOT)"
4. Open the program and click on the "Backup APNs" button.
5. After that's done, click on the "Restore APNs" button. It will prompt you to reboot your phone.
6. After the reboot, open the APNsBU program, click on the menu button on your phone and click "View APNs".
7. You should be able to see "Simple" and "T-Mobile US." Turn off your WiFi and you should be good to go!