alt Hacker NewsCan a carrier ever surreptitiously lock an unlocked phone, or is it only on phones financed or purchased through the carrier? For example, if I bought an unlocked phone and attached it to my Verizon plan, could Verizon lock it?
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notamario • today at 4:57 AM
Technically possible
Historically phone locking was done at the modem level via an NCK code - if a phone is supplied by a carrier the modem will come pre-locked and will only be unlocked upon entry of an NCK code which the carrier has the secret key to generate (hash(secret+imei)). With this system if the phone is not locked to begin with I am not aware of any way to toggle this mechanism remotely.
With smartphones however, the game has changed. Apple for example no longer locks their modems at all and instead rely on a software-level check as part of the "activation" process (at first boot where it also gets its client certificates/etc to talk to Apple services) - said activation policy can be changed remotely, and Apple are very cagey about their full capabilities. I have read of some vendors selling iPhones that would be unlocked at first but lock themselves to the first carrier they see.
It's unlikely Apple would ever enforce or change an activation policy on a phone purchased directly from them, so you should be safe. But technically, it's up to the phone manufacturer. I am not sure what the Android situation is in comparison.