I'm sure that has/will change. The new Yellow Taxi has GPS in all their cars now, to track the drivers.
Someone mentioned that you're supposed to call a cab when you've had too much to drink. Only, um, we now know the potential danger in that.
What's worse is UVA has a system set up with the taxi companies so students can call them for a "free" ride. They show their student ID, and the charge for the ride is billed to their student account.
Frightening. But who would have ever guessed?
Cabs in my area seem to maintain radio control most of the time as well as having a gps, though, not all of them. There are jitneys and offbrand cabs. A good idea to stick with a legitimate cab.