Locked

In the world of mobile phones, the term "locked" is refers to phones which are SIM locked. SIM lock, often mistaken with PIN or PUK code, is a capability that is built into GSM phones by their manufacturers. SIM lock is used by network providers to restrict the usage of the phone within certain specific countries and network providers. Currently, SIM lock is used to accept SIM cards either in specific countries (the phone will work only in one country but not any other), network/service provider (the phone will not work on any other network besides the service provider it is bought from or provisioned for, across countries) or SIM types (the phone will accept only specific type of SIM cards). Usually, locked mobile phones are manufactured and shipped are locked to a country or a network service provider.

Also a majority of modern phones feature pre-installed firmware, which allows the use of phone with SIM cards specific to the network provider. The most common SIM lock is the SP-lock or the service provider lock. The most restrictive type of lock is the full SIM card lock, which allows the phone to accept only one particular SIM card. If this particular SIM card malfunction or gets damaged, the phone will no longer work and must be serviced.