Changing the ROM frees a mobile device or not?

The short answer is no. Practically in most cases it is not possible to unlock a mobile device by changing the ROM installed on the Android device.

Unlocking a mobile device means removing the restriction imposed by an operator to work only with that company’s SIM card. This is called SIM network lock, network lock only, or “SIM Network Lock,” and it is different from the regional lock that exists on Samsung devices. The acronym ROM means different things depending on the field in which it is used: speaking of Android, it is used to refer to a firmware or Android operating system.

The network lock is commonly a software-level modification made by the manufacturer, at the request of the operator. The most common way to remove this lock (release) is to enter an unlocking code or PIN “SIM Network Unlock PIN” into the device, which can be obtained from the respective operator or can be purchased online.

Unfortunately, this lock is often foreign to the mobile operating system, firmware or ROM, therefore it remains even if you change from ROM to Android (for example, change the original operating system for the CyanogenMod system). The code mentioned above to unlock a device is associated with its IMEI identifier, an identifier whose files are located on a partition other than that of the operating system, which normally remains unchanged when installing firmware or a custom ROM.

Replacing the firmware or carrier custom ROM with a “free”, “unlocked” or “unbranded” ROM (pure from the manufacturer) will not free up a device, but will simply change the characteristics of the system (remove the operator logo during startup, remove pre-installed applications, etc.).

Based on this explanation, it can also be concluded that a unlocked cell phone (that was once locked) will not be locked again when changing ROMs, updating firmware, or restoring factory settings, as long as the unlock has been permanent type (as a general rule, when using an unlock code, the cell phone is permanently unlocked). Here it can also be noted that a cell phone reported for theft (IMEI reported) cannot be fixed simply by changing the ROM.

These are very particular cases in which it has been possible to free a cell phone by changing the ROM or installing the firmware of another operator, probably due to a “weak” method used by the manufacturer to block the device (there are several ways to implement this block, according to this information). Currently and in general, it is impossible to free a device simply by changing the Android system.