That service is provided by BMW Assist. As for the data connection it uses the available cellular network (AMPS in the past, currently GSM) and the subscriber information is tied to the vehicle.
In a phone, the SIM card provides the subscriber information and is removable, however I doubt that the SIM in the bmw is removable and may just be part of the on board circuitry since it is tied to the specific vehicle and does not need to be interchangeable.
As has already been mentioned, this is only valid for the period that your BMW Assist subscription is valid, once that expires, this service also dies with it unless you start using the annual renewal. Oh and you should definitely try out the Apps for the smartphone for the same, iphone has it in the market, android also has it in the play store, however it never showed up on any of my devices so I assumed it was not compatible, but if you can get your hands on the apk and manually install it, it might work, it worked for me.
Oh and the best thing about the apps, remote locking/unlocking!!!