Check Settings > General > About and look for “Carrier Lock” or “No SIM restrictions”
Insert a SIM card from a different carrier and see if the iPhone connects to that network
Try making a call, sending a text, or using mobile data with the different carrier SIM
Contact your current carrier and ask whether the iPhone is unlocked
Use Apple’s support or carrier account tools if available to check unlock status
If the iPhone works with SIM cards from multiple carriers, it is likely unlocked