1) Download NV reader/writer HERE and install THESE drivers.
2) Dial *#7284# and select "Qualcomm USB Settings" then check "RMNET + DM + MODEM".
*If you are running a aosp rom (cm9,cm10,aokp etc) you can use the diag method described HERE
3) Create backup.
a) Click "port" in the top left and select your samsung serial port.
b) Make sure BOTH boxes in the top bar are checked.
c) Click "Connect" in the top bar.
d) Click "Read" in the top bar.
e) Click "Read" in the lower 'NV-items' section.
f) Save the .txt file, this is your backup
*The process will take 5-10min. The file size will be roughly 3mb and "inactive item" and "bad parameter" sections are normal.
*To restore click "Write" in the lower 'NV-items' section and navigate to your backup file.
4) Dial *#7284# and select "Qualcomm USB Settings" then check "MTP + ADB".
Demonstration video HERE << Thanks to moonfire for the video.
IMEI ALREADY CORRUPT?
Use THIS custom built tool to easily generate a backup file with your properly formatted IMEI to restore your phone!
1) Enter your IMEI (find it behind your battery) in the text box up top, hit generate then hit save.
2) Use "NV-Item reader writer" to write the saved text file back to your phone and then reboot.
Time and money have been invested into this project so donations are appreciated.
ATTENTION: I need a copy of someones full backup. Requirements are that you never flashed an AOSP rom (CM9, CM10, AOKP) and that your SGS3 is T-mobile. I need this to work on the data issue!
Update: The data issue is still being worked on and some progress has been made but there is still not a solid easy fix. IF YOU MADE A BACKUP THEN GOT THE DATA BUG, PLEASE MAKE A SECOND BACKUP SO THAT I CAN COMPARE THE BEFORE/AFTER!