Open Settings
Tap General
Tap About
Scroll to Carrier Lock or Network Provider Lock
If it says No SIM restrictions, your iPhone is unlocked
If it shows a carrier lock message, your iPhone is locked
Insert a SIM card from a different carrier
If the iPhone connects and makes calls or uses mobile data, it is unlocked
If you see an invalid SIM or SIM not supported message, it is likely locked
Contact your carrier and ask them to confirm the unlock status
Check your original purchase or carrier account for unlock information