Open Settings
Tap General
Tap About
Find Carrier Lock or Network Provider Lock
If it says No SIM restrictions, the iPhone is unlocked
If it shows a carrier lock, the iPhone is locked
Insert a SIM card from a different carrier
If the phone works with the new SIM, it is unlocked
If the phone shows SIM not supported or similar, it is likely locked
Check with your carrier using the IMEI number
Use the IMEI on the carrier’s unlock status page if available
Contact Apple Support for device details if needed