My phone says SIM card locked

After the wrong SIM code is entered too many times, it will ask for the PUK code. This code is also only available from the carrier. If the wrong PUK code is entered too many times, it will make the SIM card invalid and will require a new SIM card from the carrier.

There is no way to reset the SIM code. The carrier is the only one that can provide that for you. It may require a trip to a local AT&T store if they are unable to give you the information over the phone.

If the SIM card is just showing Locked in the settings, but you are still able to use your phone, then that just means that the phone is locked to AT&T so you can't change carriers.

If your iPhone is displaying a message that your SIM card is locked, it’s likely related to the SIM PIN for your card. This is a feature that can prevent unauthorized use of your SIM card, such as if your phone is stolen.

Here’s how you can unlock the SIM card on your iPhone:

1. Go to “Settings” on your iPhone.

2. Scroll down and tap on “Cellular”.

3. Tap “SIM PIN”.

4. Enter your current PIN (if you haven’t changed it, the default SIM PIN for AT&T is 1111).

5. Switch the “SIM PIN” switch to the OFF position.

This should unlock your SIM card. If you’re still having issues or don’t know your PIN, I would recommend contacting AT&T again and ask for further assistance. They should be able to help you unlock the SIM or provide a PUK code to unblock it if the PIN has been entered incorrectly too many times.

Well, everything is good at AT&T's end. The phone is locked to their service so that prevents you from moving to another carrier.

If you do want to move to another carrier, you will probably need to ask AT&T to release the lock on the phone. Apple is not involved.

There is nothing anyone at Apple or this user to user forum can do for you. You need to escalate the call at AT&T to someone who knows how to fix it. AT&T is the only one who can.