Check that the phone is paid off and not reported lost or stolen
Make sure the device has been active on AT&T for the required period
Confirm the account is in good standing with no past-due balance
Get the phone’s IMEI by dialing *#06#
Go to the AT&T Device Unlock portal
Select the device unlock request option
Enter the IMEI and requested account details
Submit the unlock request
Wait for AT&T to approve or deny the request
Follow the approval instructions sent by email or on the portal
Insert a SIM card from another carrier or complete the unlock steps on the phone
Restart the phone if needed
If the request is denied, resolve the listed issue and resubmit the request