TC,
We have the system that you refer to here in Australia, I have it fitted to one of my cars. "Holden Assist", otherwise known as Telematics System, which tracks via GPS and GSM phone: it can immobilise a running engine (slowly, not a sudden cut out), unlock the doors, and interrogate the occupants of a car via the phone. The latter is to verify (via password) that the car hasn't been nicked; I also get occasional calls to let me know when the battery is getting low
A well publicised car theft in Melbourne had everything work to order after a thief took the owner's keys and made off with the car. Owner called in the theft to Holden & Police, the location was established and passed to the cops. The car was found and chased through town, then immobilised. Only snag, no one told the coppers that they could have the car unlocked remotely, so they took the trusty batons out, and belted in the car windows to gain access!
I believe the same set up is available in the USA.