If you don't have the key, how? I browsed XDA forums a lot in the past to try and ulock and old phone, and there didn't seem to be any way. All of the guides ended up being nonsense.
Someone above said you need the NCK code which is generated from a secret only the carrier has - how does having root get around this?
The lock is basically implemented as an "is the SIM's carrier on a whitelist" check, which can obviously be patched out or modified arbitrarily once you have full access to the firmware which root does. It's important to remember that the lock is entirely on the phone's side, to prevent it from connecting to any other carrier than the one it's locked to. A carrier can implement an "official" unlocking method essentially as an app that runs on the phone to validate the unlock code, but that is no obstacle to root.
If you jailbreak an iPhone, the lock is also easily removable in the same manner.
If we're talking NCKs it means the modem is locked, so you need a modem/baseband-level exploit. Root helps you talk to said modem but doesn't directly allow you to modify its firmware without some other exploit.
Not really familiar with other platforms, but on Mediatek platforms the modem firmware is just loaded from the filesystem --- which you have full access to as root.
Can you recommend any good guides to read more about this? I was trying to unlock a Boost phone a few years ago, which was perfectly good and compact but unusable outside of Boost. I no longer have the need but still have the curiosity.
Someone above said you need the NCK code which is generated from a secret only the carrier has - how does having root get around this?