SIMlock is a blocking code for the restricted use of SIM cards. This blocking code prevents a mobile phone of a SIM card or a prepaid card of a certain service provider
or network operator from being operated with a SIM card of another network operator. Providers can also use it to restrict the use of certain services, for example, it can prevent the use of prepaid cards from other service providers, the use of the mobile phone in certain countries or networks. The latter, the blocking of certain networks is called Netlock. Only after the blocking period has expired can the blocking code be lifted by the network operator
. Such a blocking is called a netlock.