Ten unsuccessful unlock attempts permanently locks the device to the AT&T network.
1. Switch the device off.
2. Remove the AT&T SIM card.
3. Insert a non-AT&T SIM card.
4. Switch the device on. If prompted, enter the SIM PIN code.
5. Wait for the SIM unlock window to open.
6. Enter the unlock code provided (8 or 20 digits) and press Enter.
7. Power the device off.
8. Power the device on. The device is unlocked.