Check the SIM card from another carrier; if the phone rejects it, the phone may be locked
Look for a “SIM not supported,” “Invalid SIM,” or “Network locked” message
Go to the phone’s settings and check carrier or network lock status if available
Contact the current carrier and ask whether the device is locked
Use the phone’s IMEI with a carrier or IMEI check service to verify lock status
Try making a call or using mobile data with a different carrier’s SIM
Check whether the phone was sold as “carrier-locked” or “unlocked” in the purchase details
On iPhone, check Settings, General, About, and look for Carrier Lock or Network Provider Lock
On Android, check SIM status or network lock information in the device settings if supported
If the phone only works with one carrier’s SIM, it is likely locked