I don't remember seeing car locks under any OBDII connection, newer, or older. And if it would be available through VWs protocol, I doubt it is going to under every things elses.
As for power, I think there is a thread in the OBDII forum. Search there for help on that.
It sounds like a really cool project, I thought you needed a license or a subscription for GPRS though, so I don't know how many people are going to be able to take advantage of it.