How can I unlock my iPhone 5 on iOS 6.1.3 without updating to iOS 7

Question

My iPhone 5 is approved by AT&T to be unlocked. It's currently running iOS 6.1.3. I have yet to restore it via iTunes to complete the unlocking process due to the fact that its says that it will update it to the new iOS 7. Is there a way to restore my iP5 so I can unlock it while maintaining iOS 6.1.3?

Answer 1

I have tried this method on two different iPhones while using different computers and AppleID's.  Here is the method I used to successfully unlock the iPhone without upgrading to iOS 7.
Both phones were the iPhone 4 model.
Both phones were using iOS 6.x.x
I called my provider and asked for the phones to be unlocked.
They told me that the IMEI was entered into Apple's servers and I just need to connect to iTunes to unlock.
Both unlocks were done through iTunes, one on an iMac, the other on a MacBook Pro.
Step 1: Backup the iPhone using iCloud or iTunes as desired
Step 2: On the iPhone, go to Settings:General:Reset:Reset All Contents and Settings
Step 3: Allow iPhone to complete the reset and wait for it to restart
Step 4: Plug iPhone into computer and wait for iTunes to start (or start it manually)
Step 5: Message will pop up to either Set up as New Phone or Restore from Backup
- at this point I was expecting the "Congratulations you are Unlocked" message, but it did not appear so I disconnected the cord to the computer and continued.
Step 6: Disconnect Sync cable, on the iPhone, go through basic setup... skip any steps it will allow you to skip.
Step 7: Go to Settings:General:Reset:Reset All Contents and Settings
Step 8: Allow Phone to reset and restart but do nothing else on the phone
Step 9: Connect to iTunes again
Step10: Message appeared, "Congratulations, Your phone is now Unlocked"
Step11: Restore your previous backup from iCloud or iTunes
This method worked for me more than once.  Both times I had to connect the iPhone to iTunes twice in order to get the unlock message.
Hope this helps.
Original message: in response to apple-id