How to check if your phone is carrier locked

Open Settings, then General, then About. Look for Carrier Lock (called Network Provider Lock on some versions). "No SIM restrictions" means the iPhone is unlocked. Any other message means it is still tied to a carrier.

Power the phone off, insert a SIM from a different carrier and power it on. If you see messages like "SIM not supported", "SIM network unlock PIN" or "Invalid SIM", the phone is locked.

If the phone connects and you can make a call, it is unlocked for that network.

On many Android phones, open Settings, then Connections or Network, then Mobile networks, then Network operators. If the phone only lists its original carrier and cannot search others, it may be locked. The SIM test above is the most reliable confirmation.

An IMEI check report can show the original carrier, lock status and whether the device is reported lost or stolen or has unpaid bills (blacklisted). This matters because a blacklisted phone may not work on any network in some countries even after unlocking.

First ask the original carrier: many will unlock a fully paid device for free. If that is not an option, a remote IMEI unlock service can process the unlock using only the IMEI, with no software to install on the phone.