Nokia Lumia 521 Go to product viewer dialog for this item. , primarily sold through and MetroPCS (now Metro by T-Mobile), is often carrier-locked. Unlocking it allows you to use SIM cards from other GSM carriers. How to Get an Unlock Code
To unlock your device, you need a specific unique to your phone's IMEI number. Metro by T-Mobile Phone Unlock Policy Unlocking Codes For Nokia Lumia 521