Check Settings > General > About and look for “Carrier Lock” or “No SIM restrictions”
Insert a SIM card from a different carrier and see if it works
Try an eSIM from another carrier and see if it activates
Contact your current carrier and ask if the iPhone is unlocked
Check your original purchase receipt or carrier paperwork for unlock status
Use Apple Support or the carrier’s online device status tools if available
If the phone works on multiple carriers, it is likely unlocked