Check that your device is eligible for unlocking
Make sure the phone is paid off in full
Confirm the account is in good standing
Remove any active installment plan or contract obligations
Get your IMEI number by dialing *#06#
Submit an unlock request through the AT&T Device Unlock Portal
Wait for AT&T to review and approve the request
Follow the instructions in the approval email
Insert a SIM card from another carrier after unlocking
Restart the phone if needed to complete activation