Fact Checked

What is a SIM Lock?

G. Wiesen
G. Wiesen

A SIM lock is a function built into many mobile telephones that allows phone service providers to lock a phone so it can only be used under certain circumstances. These circumstances are typically involved with retaining phone service, such as only allowing the phone to work in certain countries or on networks provided by a specific company. This locking function is connected to the Subscriber Identity Module (SIM) provided with the phone and ensures that the phone can only be used in a way the service provider wishes. A SIM lock can be unlocked by the company that provides the phone service or by using a number of different third-party applications.

Also called a “simlock” or network lock, a SIM lock is usually meant to ensure that customers who purchase a phone from a particular company continue to use that company’s services. Unless unlocked, a card that is locked will typically work only with the network provided by a particular company or in a certain region. This is done to encourage customers of a mobile service provider to remain loyal to that provider in the long run. Phones that have a SIM lock may also be less expensive than unlocked phones, since they typically ensure that the customer purchasing the phone only uses the network provided by the selling company.

SIM card.
SIM card.

The SIM lock on a phone is typically associated with the SIM card provided with the phone, meaning a customer using a particular mobile provider will be locked on any phone he or she uses with that card. SIM cards allow customers to transfer their information and phone service between different phones. The SIM lock on these cards allows providers to ensure that a customer continues to use their service while under contract.

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

Most mobile network providers can unlock a SIM lock if asked to do so by a customer. There are typically no statutes requiring that providers do so, however, so it is up to a company to decide whether a SIM card should be unlocked. Even once unlocked, the phone may still retain firmware associated with the service provider, such as menus and operating systems. This is why an unlocked phone may still display the logo for a certain service provider on startup.

A phone with a SIM lock.
A phone with a SIM lock.

A phone with a SIM lock can also typically be unlocked using third-party programs and services. The legality of such services is somewhat questionable, but typically is allowed though such companies may charge a sizable fee. Information provided by a person to have a SIM card unlocked can also potentially be used by someone else to spoof the person’s phone information. This could allow someone else to use his or her service and could lead to legal complications or service cancellation in the long run.

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Discussion Comments


I need to unlock a sim locked phone. The phone is US cellular.


Depending on the phone, using an online code to remove a SIM lock does not always work. This can also be a way for people to spread malicious software to a person's phone. Because of this, it is typically best to get an official code from a phone company.


SIM lock is a network lock. If your mobile is locked to a network then you won't be able to use other network SIM in your mobile. To use other network SIM we need to remove the SIM lock by getting the unlock codes. You can get the codes online.

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    • SIM card.
      By: Nikolai Sorokin
      SIM card.
    • SIM card being placed into a mobile phone.
      By: Brian Jackson
      SIM card being placed into a mobile phone.
    • A phone with a SIM lock.
      By: schankz
      A phone with a SIM lock.
    • Some sim cards are packaged inside of a larger card in order to protect them from damage before use.
      By: Iaroslav Neliubov
      Some sim cards are packaged inside of a larger card in order to protect them from damage before use.