When we talked about how a SIM card lock works, we mentioned network locking as one of many methods. To ease your worries, we’ll tell you it’s not anything you might have done, i.e., it isn’t a result of our guide for locking a SIM card on Android, iOS, or iPadOS. With that said, we ought to say that you can still do something against it. It may be a hassle and will likely cost a bit, but you may circumvent the protection the network imposed. Now, let’s dive straight into the answer to the question, “what is a network locked SIM card?”
Explanation of a network locked SIM card
SIM (Subscriber Identity Module) cards that networks lock, also known as carrier-locked SIM cards, represent those SIMs that have the technological capability to work on all networks, but are modified to only work with one. It surprised no one that the carrier, i.e., the mobile network provider is the one that modifies them before giving them out to users. However, that situation is not as frequent and sometimes impossible because it required memory editing on the IC (Integrated circuit) chip, which can be expensive and time-consuming. After all, large carriers need to ship millions of SIMs to users, and the modification procedure must be tailored. We’ll explain the drastically more common alternative shortly.
Regardless, once you insert it and unlock the PIN (Personal Identification Number), you would get a message, “Invalid SIM card. Network locked SIM card inserted”. Sometimes the menu doesn’t let you do anything. The carrier won’t permit proceeding without contacting them and paying. Other times the option demands you enter a PIN, but different from the regular one. It is the so-called Network Unlock Code (NUC) or Mobile Network Code (MNC).
Carrier locking the device rather than SIM
However, another, more common cause is a network-locked device rather than a SIM card. That means the device you have was locked by a network provider, preventing SIM cards from any other but theirs to access the network.
That is done via software, by modifying the firmware or adding a hidden application. In doing so, the carrier prevents the device from using any other SIM card but theirs. They also add unlocking key users or their clerks must enter to remove the protection. Depending on the country, locking may be forbidden, allowed for a limited period, say 2 years, while the contract is active, or unrestricted. To sum up, your device or SIM card is locked by the mobile network provider that provided them, and you need to contact them for an unlock key.
Why do carriers lock SIM cards or devices?
The reason a mobile network provider locks a device or a SIM card comes down to one thing: keeping customers for profit. They may do so to prevent postpaid carriers from using discounts when buying a payment plan and a device, then inserting the SIM card from another network and never spending. The same applies to carriers who reduce pricing around holidays or sell expensive premium packages with limited validity to account for the cost shrinking.
We can debate using SIM card reader and writer devices to program SIMs to only connect to one network. Most say it’s for security reasons, but there are no apparent benefits to locking phones for customers. Some users whose devices were stolen and returned credit that fact to the thieves being unable to use any other SIM. However, you can protect access to your network-unlocked device in other ways. Additionally, nothing stops thieves from using the black market. They can also sell the device for parts or to someone with a fitting SIM card carrier. Therefore, there are no notable advantages to network-locking of SIM cards for users, only protecting carriers’ interests.
Can you unlock a network-locked SIM card?
We already wrote a SIM card unlocking guide, and our “Carrier lock” section tells you that bypassing the lock on a carrier-locked SIM card is possible. We already covered sending requests to carriers to provide a Network Unlock PIN (NUP). However, to avoid confusion, depending on the country and provider, NUP may also be called:
- Network Unlock Code (NUC)
- Network Control Key (NCK)
- SIM Network Unlock PIN
- Master Unlock Code (MUC)
- Network PIN
As you can see, you can contact a carrier. Then, depending on the terms, you must pay a fee or send a free request. Alternatively, you may hire a third-party service to perform unlocking. However, that guide only covers Android-based, feature, and old phones. Users of iPhone and iPad devices must check our “jailbreaking a SIM card” article. Android users can also check the guide for a revolutionary method that includes an XSIM card. In short, XSIM is a custom SIM card MOS chip. When inserted into the mobile device, it opens a custom menu with preprogrammed unlocking codes.
After selecting your model and make during booting, the chip will load those codes. It will then unlock the device to any carrier in the world. The only downside is that you may have to reenter your ICCID (Integrated Circuit Card Identification) number every time you update the operating system. Speaking of which, in rare cases, you may get a “This SIM card is network-locked” error due to firmware problems or a faulty network antenna. Therefore, doing a factory reset, downgrading firmware, or taking the device for repair may be the only solution.