While it's not quite on topic, this presentation by moxie marlinspike last year at defcon europe has some interesting thoughts on how we voluntarily surrender our privacy. It's definitely worth a watch if you're thinking about the subject.
This obviously wouldn't prevent against a targeted attack. If the phone company or the government wanted to track YOU specifically, they could probably figure out your phone number by looking at the calls your family and friends have made and finding the union, and retrieve the info from there.
But if someone wants blanket info, i.e. a list off all the people at a G-20 protest or whatever, a computer won't be able to instantly figure out who you are. Someone would have to start investing real man-hours to accomplish this. This hopefully gets too cost-prohibitive for large scale tracking of the general population.