Open Settings
Tap General
Tap About
Find Carrier Lock or Network Provider Lock
Check the status
If it says No SIM restrictions, the iPhone is unlocked
If it shows a carrier name or SIM locked, the iPhone is locked
Insert a SIM card from another carrier
See if the phone connects to that carrier’s network
Make a call or use mobile data with the other carrier’s SIM
Contact your carrier and ask them to confirm unlock status
Check the original purchase or carrier account details for unlock confirmation