Here's how to unlock your iPhone with a single SIM (updated for iOS 7):
Enjoy your new carrier options
- If your locked AT&T iPhone is near its contract expiration go here: https://www.att.com/deviceunlock/client/en_US/termsAndCondition
- Fill out the form, ignore the AT&T Account Passcode and click "Submit"
- In a few minutes you'll receive an email confirmation from AT&T that says "We have reviewed your request and confirmed that the device may be unlocked."
- Wait 24 hours before proceeding to the next steps
- If you have another carrier contact them to unlock your iPhone when your contract has ended
- On your iPhone tap Settings
- Scroll down and tap iCloud
- Disable Find My iPhone
- Remove your iPhone's SIM (you can use a straightened paperclip or push pin)
- Connect your iPhone to your computer's USB cable
- In iTunes under "Backups" > "Automatically Back Up" click "This computer" (not "iCloud")
- Click "Back Up Now"
- In the menu bar click "File" > "Devices" > "Transfer Purchases from 'your iPhone'"
- Click "Restore iPhone" (not "Restore Backup") and click "Restore"
- iTunes will display the message "There is no SIM card installed in the iPhone you are attempting to activate. Please disconnect and insert a SIM card in the iPhone."
- Disconnect your iPhone from the USB cable
- Insert your iPhone's SIM
- Wait a minute for your iPhone to display the "Hello" message
- If it's still stuck on the "No SIM Card Installed" message power off and power on your iPhone
- Connect your iPhone to your computer's USB cable
- iTunes will display the message "Congratulations, your iPhone has been unlocked."
- Click "Continue"
- Ensure "Restore from this backup" is checked and click "Continue"
- Wait about an hour for the restore to complete
- On your iPhone tap Settings
- Scroll down and tap iCloud
- Enable Find My iPhone
Enjoy your new carrier options