This document created at Jun 23, 2020, 1:47:22 PM and modified at Dec 30, 2020, 1:23:41 PM.
What is carrier relock and how does it work, specifically?
What is carrier relock?
Carrier relock is similar to an unlock, except instead of unlocking it for all carrier's sim cards,
you are relocking it to the carrier sim cards of your choice. When doing a carrier relock, the phone will
behave as if it is unlocked, whenever you insert a sim card that is included in the carrier relock list.
You have the possiblity of adding up to 64 different carrier sim cards on your carrier relock list.
How does it work, specifically?
Every sim card has a MCC (mobile country code) and MNC (mobile network code). When a phone is programmed
from factory, the unlock codes are programmed, as well as a list of MCC/MNC pairs, which the phone will
be locked to. Whenever you insert a sim card which is not in this list, the phone will request the unlock
code, or it will display a type of message indicating that your device is locked and sim card cannot be
used. Essentially we are replacing the factory list of MCC/MNC, with a list of our choosing, so that a
large amount of sim cards can be used, without requiring the unlock code.
Why can't we do a full unlock, instead of a carrier relock?
This service was added for a specific kind of security, in which it is very difficult to unlock the device
via regular means. It is a cost effective way of being able to use the phone with the sim cards you wish to
use on them. If a stable and working method for full unlock can be found, be assured that it will be added.
Until this moment, carrier relock is the only method that can be offered for these devices.
Why is the device still not working, with the carrier relock list I've chosen?
If the process completes successfully, it means that the phone has accepted the new carrier relock list.
If for some reason, it is still not working, the most likely scenario is that you have omitted the
MCC/MNC for the sim card that is inserted into the device. You should find the MCC/MNC of the sim card first,
then add it to your carrier relock list, and re-attempt the carrier relock operation.
How can I find the correct MCC/MNC for the sim cards?
Many carriers utilize different MCC/MNC, even though they run on the same cellphone network. There can be
many reasons for this, such as different sim card revisions, new sim card functionalities, etc. Fortunately,
it is not too difficult to find the MCC/MNC for the sim card. It will require inserting the sim card into
another unlocked android device. There are a couple of methods, you can select which is easiest for you.
1) Open Settings app, select Connections, Mobile Networks, Access Point Names, and then select any of the
APN options that show up for the inserted sim card, or if none appear, choose the Add option. You will
find the MCC and MNC in this menu, when scrolling down.
2) If you are famility with adb commands, you can get the MCCMNC by the adb command:
'adb shell getprop gsm.sim.operator.numeric'. The first three digits are your MCC, the rest is your MNC.
3) You can install and open an application such as SIM Data Reader, from the Play Store. The MCC and MNC
will be shown here as well, after giving the application the permissions it needs.
Why does the carrier relock operation not work on my device?
Samsung occasionally makes small changes to the way their modem works. Unfortunately, one of these changes
they made, affected the ability for carrier relock to work on Qualcomm devices. Any Qualcomm device, with
security patch of 01/02/20 or newer, will not work. You can attempt to downgrade, if it is possible to do
so on your device, then retry the operation. Exynos devices have not been affected by this change, as of
the posting date of this F.A.Q.
Does the carrier relock operation survive hard resets, factory data resets, firmware updates?
Hard resets, factory data resets, and letting the phone take an update, does not cause the relock operation
to go away. However, it is possible that the contents of the firmware update contain new modem code, that
alters the way carrier relock works.
Unfortunately, Samsung has full control over their devices, with ota updates. If they wanted to, they could
brick your device, or make it not work with any sim cards at all. So we have no control, and no way to know
what they can include in their updates. Qualcomm devices suffered this fate, but Exynos has been unaffected.
The only normal way that can possibly alter the carrier relock is by attempting the Permanent Unlock in Settings.
When this happens, the device contacts an external server, to check for unlock eligibility. If it is eligible
for a full unlock, the device will unlock. However, if it is not eligible, the external server will reprogram
your device with the default carrier relock list. But not to worry, you can simply re-run the operation,
in the case that this happens.
This will be the number one case, for shop owners that have clients come back with
a device that was carrier relocked. The client "did nothing", but rest assured, that they likely messed with this
setting. During the operation, the app/package responsible for allowing this Permanent Unlock option will be
disabled, so that it cannot be accessed. However, occasionally this application will be re-enabled, if the phone
is wiped, for example. You can disable the package manually again, in this case, if you wish.
How can I disable the package responsible for allowing the Permanent Unlock option to appear, to prevent issues?
This requires an adb command. The adb command to run is: 'adb shell pm disable-user --user 0 com.samsung.ssu'.
If you wish to disable ota updates, as well, you can find instructions for this on google.
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