How to check carrier lock status on Android devices

1. Access Settings from the drop-down menu or your App Drawer
2. Tap on Connection, Network & Internet, or similar, depending on brand and model
3. Select Mobile network, Cellular network, or similar, depending on brand and model
4. Tap on Advanced (if required) and select Choose Network, Automatically Select Network or similar, depending on brand and model, to open the list of carriers
5. If several carriers appear, your phone is most likely unlocked and just needs the appropriate Sim card
6. Remove the old SIM card from your phone and insert the newly activated one from another carrier. Try using mobile data to browse the Internet, but make sure that WiFi is disabled
7. If this works and you can access the Internet, your phone is indeed unlocked

You can also call your present carrier to confirm the locked/unlocked status of your contract with them.