What is simlock? (EN)
A simlock is a feature included by mobile phone makers or providers to enable only the use of certain types of SIM card in that handset. At the moment, phones can be locked, so they only accept a SIM card from a particular country or set of countries, one particular network, or one provider.
The system is designed to stop you from operating your mobile under another SIM card. It can prevent you from making phone calls or surfing the mobile Internet abroad. It is one the main reasons a mobile user will be greeted with the message: Insert correct SIM card.
The reason for phone locking is generally commercial in nature. It enables operators to sell affordable pay-as-you-go handsets. Arguably, this is not such a great deal for the consumer, however. The good news is that it’s not too difficult to unlock a phone if you decide to go down that route.