Note that this will remove your cwm recovery installation if you have one. You will have to nvflash your phone again. And of course I am not responsible for any repercussions that may occur by you following this guide.
- Backup all apps + data.
- Download the cwm backup stock wind firmware, a kdz file with the v21y baseband and the vbscript installation archive.
- Extract wind firmware archive in clockworkmod/backup.
- Boot into cwm recovery.
- Clear data and cache.
- "Recover" wind firmware from backup.
- Boot into the new wind firmware.
- Extract vbscript installation on PC and follow the directions from the download page. There's only one thing you do different: don't change the "Diag" menu to "EMERGENCY". Diagnostic mode is for phones that are powered on, emergency is for s/w update mode (volume down + power).
You are now running T-Mobile gingerbread with the v21y baseband! Now you can nvflash cwm recovery again and install your ROM of choice!