This is a complete quote from the relevant section of http://stallman.org/rms-lifestyle.html
I refuse to have a cell phone because they are tracking and surveillance devices. They all enable the phone system to record where the user goes, and many (perhaps all) can be remotely converted into listening devices.
In addition, most of them are computers with nonfree software installed. Even if they don't allow the user to replace the software, someone else can replace it remotely. Since the software can be changed, we cannot regard it as equivalent to a circuit. A machine that allows installation of software is a computer, and computers should run free software.
When I need to call someone, I ask someone nearby to let me make a call.
As a ham radio operator myself, reading some on GSM and other standards, a little on OpenBTS, and what the military (especially black ops like CIA) have done in these kinds of situations, I think I can reliably state this:
1. *ANY* radio transmission can be tracked to its source. If your phone on, it can be triangulated automagically by the base stations around you, although modern E-911 compliant ones also assist in this. In addition, the TIMING can be used to trace your distance from even one cell site (think latency/ping), so you can get a radius (similar to GPS, if I've read right).
2. The only way not to be tracked in this fashion is to turn off all radio transmitters on your person or nearby that can be associated with you. This includes wifi and can even include bluetooth in radio-quiet locations. Bear in mind you can fingerprint individual transmitters, to the point there are commercial transmitter fingerprint readers readily available: these are usually used when dealing with jammers, but you can track anyone with these.
3. None of this precludes them putting an active tracking device in your phone (I've read the battery can be replaced with a smaller one with a device included), your car, jacket, etc. These were being done during the cold war; the only difference is that you can buy them online now! And don't even get started on passive methods like lasers-on-the-windows, Van Eck, etc.
4. Jamming just keeps you from making calls: your radio can't hear the base. The base can still hear you just fine (under normal circumstances).
The bottom line: you'd have to do like RMS does and not carry one...though I wonder how useful that is since his entourage probably are loaded with them!