How to check if my iPhone is carrier locked or unlocked?

Goto settings on the iPhone, then General, then About.

Scroll down to where the Wi-Fi address is shown.

6 items below that have an entry that says;

Carrier Lock, if it shows “no SIM restrictions” the phone is not locked to a specific cellular provider and can be changed to other cellular providers.

Hope this helps with your question

Hi there. Are you getting an error message that your iPhone is locked? If yes, please check the link below:

If your Apple ID is locked or disabled - Apple Support

What is the message that appears on your iPhone?