What Is SIM Unlocking?

Andrew Kirmayer

Many mobile phones have a Subscriber Information Module (SIM) that identifies the phone as belonging to one service provider in a particular country. These phones are programmed to work with certain SIM cards before they are purchased. SIM unlocking will change that programming either by entering a code into the phone or by changing the software. Changing the cards will enable one phone to work in different countries or with the services of different providers. A mobile phone owner can benefit from SIM unlocking because he or she can still use their phone after changing providers, or keep the old phone in case something goes wrong.

SIM card.
SIM card.

If a phone or card has not been unlocked by the company, there are a couple of ways it can be done. A code, which identifies the phone’s serial number, is typically required for SIM unlocking. Codes can be found for specific models of phones and are sometimes sold by service providers or other companies. If the phone’s software needs to be changed, then a specific cable and machine to program it are needed. This process can also be provided as a service performed for a fee.

SIM card being placed into a mobile phone.
SIM card being placed into a mobile phone.

Phones are programmed to alert users if a restricted SIM card is put in. Swapping cards will determine whether a particular phone is unlocked. If a code or software upgrade has unlocked a phone, there should be a message that says so once the procedure is completed. Another way SIM unlocking can be done is to send the phone to the manufacturer or phone company, which is generally completed for a fee.

In some cases, companies will unlock phones when they are purchased. If the phone is unlocked later by the user, then the warrantee may be voided and the company will no longer service the phone. The SIM unlocking technology, however, does not do anything to change the function of the phone or improve the reception. If a phone user changes providers, there is the chance that a new service company can re-lock the phone, even though the device doesn’t belong to the company.

In the past it was considered illegal by some regional authorities, but SIM unlocking is often legal to perform as of 2011. It is occasionally beneficial to use a different SIM card, especially if the phone is used in another country than where the user lives. Users can also keep their phones even when changing providers. An unlocked SIM card also lets a someone keep the old phone as a backup, so he or she can insert the card in that device if something goes wrong with the first.

Some sim cards are packaged inside of a larger card in order to protect them from damage before use.
Some sim cards are packaged inside of a larger card in order to protect them from damage before use.

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