Just because I spent so much time looking for this last night and found so many broken carrier data files, I figured I’d keep this around for me.
Instructions
- Make a backup of your /Library/iTunes/iTunes Carrier Support/ATT_US.ipcc file.
- Quit iTunes
- Open Terminal and type “defaults write com.apple.iTunes carrier-testing -bool TRUE”
- Open iTunes, select your phone and press “check for updates” while holding down the ‘Alt’ key on your keyboard. You will be prompted to select a file. This is the one that worked for me after numerous other failures. (found in gizmodo’s cache somewhere)
- After you load the file, make sure you restart the phone
Instructions for Windows are the same, but you’ll have to use the Windows Paths for stuff (C:\Program Files\iTunes\blah blah blah).
Right, and I’m not responsible for you running up a trillion dollar bill with AT&T or if your spine curves or if your teeth yellow or if you drink rat poison because you fell in love with a rough trick named Jim or anything else as a result of you trying to do something to your bejebus phone 
