Technicians in the tracking station can, if necessary, track a particular call back to the cell site from which it originates. But the monitoring can not be done unless the phone is in use. [ Is that true? ]
There is an optional mechanism called "registration" by which the system can keep track of your approximate location even though you're not actually making calls. The intent is not really to track your location, although it could certainly be used for that purpose. It's intended to minimize the amount of "flood paging" that goes on. When somebody calls you on a cell phone and the system doesn't know where you are, it has to broadcast the page (the message announcing the call) on every cell in the system. In large busy systems, this can cause quite a bit of congestion on the paging channels. So the system has the option of asking the users to transmit occasionally so the system can keep track of their location and direct incoming pages to the last known cell, at least as a first try. Think of the system as a large bridged Ethernet and you won't be far off, at least on the concept. On the other hand, the fact that most cell phones see very little use, and the use that they do see is predominantly mobile originated, means that registration actually doesn't buy that much in practice. It can even be counterproductive because of all that non-revenue generating registration traffic that takes up capacity on the access and paging channels. This probably explains why registration isn't often used in practice, as far as I know. The best way to make sure it isn't occurring, of course, is to turn off your phone. Phil