Check whether the phone accepts SIM cards from different carriers
Insert a non-original SIM and see if it connects to the network
Look for a “SIM not supported,” “SIM invalid,” or similar message
Check the phone’s settings for carrier lock or network lock status
Contact the original carrier and ask if the device is locked
Use the phone’s IMEI with a carrier lock checker
Test whether mobile data and calls work with another carrier’s SIM
Compare the phone’s purchase source to the carrier it was sold through
Ask the seller directly whether the phone is unlocked
Try activating the phone on a different carrier’s network