I was reading https://reverseengineering.stackexchange.com/questions/15011/how-does-a-sim-card-work and from that, I can say that, really really simply put, a SIM card is sort of an extra memory that allow the phone to hold data that the carrier can use to communicate with.
Now let say the carrier deactivate a SIM (for instance a SIM that was not used for a REALLY long time). I'm asking myself what could be done with that SIM. Sure IMEI for instance in written inside the SIM. But it is not mapped to any carrier phone number anymore. The carrier only know of the existence of the SIM at this point, not its activity.
So what can be done with the SIM to make it work without having to reactivate it from the carrier for instance ?
Or what other activities (programming wise) can be performed with the SIM at this point that for instance can make it work with a different carrier, sort of making it a stealth SIM on any carrier ?
I'm not asking for implementation details…. I'm just wondering if at all possible.
For instance when you buy a PC, if you Windows licence does not fit you purpose, you can flush the HDD and install a new OS, Windows, Linux, etc…
Best Answer
The SIM card contains the IMSI (International Mobile Subscriber Identity) number and the associated private key. The IMEI (International Mobile Equipment Identity) is part of the phone.
Basically, the IMSI is the user name, and the private key is used similar to a password here. You can reuse that SIM card only when you find an operator willing to accept your account data.
Commercial operators just give you a new SIM card, as it is way cheaper to give you an envelope than to read the IMSI off your card and reactivate it.
What you can still do is read (and write) the phone book and SMS store on the card.