To check if your phone is carrier-locked, follow these steps:
For iOS Devices (iPhones and iPads):
Open Settings.
Tap General.
Select About.
Scroll down to find Carrier Lock or Network Provider Lock.
If it shows the name of a carrier, your phone is locked to that carrier.
If it says "No SIM restrictions," your phone is unlocked and can connect to multiple networks.
For Android Devices (Samsung, Google, etc.):
Open Settings.
Tap Network & Internet or Connections.
Select Cellular Network or Mobile Network.
Go to Advanced and then choose Choose Network or Automatically Select Network.
If only one carrier is displayed, your phone is likely locked to that carrier.
If multiple carriers are available, your phone is unlocked.
If your phone is locked, you'll need to contact your carrier to have it unlocked.