Why is my Samsung saying Network locked SIM card inserted?
If you originally received your device from one network provider and your new SIM card is from a different network, the original network provider may have locked the device to their network. Samsung does not lock any of its devices to any particular network.
Can you unlock a network locked phone?
When a handset is locked it means it will only work with the provider that you bought it from. If your phone is locked it won't automatically become unlocked when your contract expires with your provider. You'll have to specifically ask your carrier to unlock it.