How to find who my carrier is

The carrier is the company that you pay your cellular service bills to.

You can also remove the SIM card on your iPhone and then check the carrier’s name on it.

If you have active cellular service on your iPhone, then the carrier name will appear on the top left corner of the Lock Screen.

Axel F.

You say your phone is locked. If you just bought this phone and found it is locked ((SIM not supported) there is no way to find out which company locked it without asking the previous owner.