I got to play with these in Afghanistan. They were installed in our SUVs but they were so huge and unwieldy. I'd be interested in seeing what setup he had. Unless the traffic was very dense and slow, I'd imagine him just forcing calls to be dropped as he passed by which doesn't really seem helpful. Restaurants/theaters/anywhere-there-be-tweens, yeah bring it on in those locales!
They're (cellular frequency jammers) down to the size of a cigarette pack, and can run off 12V aux power in your car. Range isn't terribly great (~100ft).
Mods: I posted the link (which was the first google result for "cell phone jammer") just to show what the size and cost was. If it needs to be removed, please feel free to remove my comment in its entirety.
A friend has one of these compact models from China, and it works just as you'd expect. It will completely kill any and all cell phone connections (or WiFi, or Bluetooth) within a large room. Apparently it can run for several hours on battery, or the length of a long movie.
Historical aside: during the 'Troubles' in my part of the world, the creators of radio-triggered devices soon became wise to jammers and inverted the logic so that they detonated when a continuous signal was lost due to jamming.
You can do network-specific jamming really easily (P25, the dominant digital trunked police radios, can be locked out by reprogramming a toy pager to tie up the trunks, for about $20 and in the milliwatts...).
JIEDDO was generally trying to jam more than just cellphones, and wanted high assurance, and while they were in motion (so, you needed range).
I imagine you already know, but for everyone else, the full comedy of the P25 system can be found in "Why (Special Agent) Johnny (Still) Can’t Encrypt"[1] by Clark, Goodspeed & others.
Chapter 4 covers the DoS using a kid's wireless IM gadget
Also:
> "All users operated in the clear, but
gave an indication that they believed they were operating in encrypted mode. In some cases, this involved one user explaining to another how to set the radio to encrypted mode, but actually described the procedure for setting it to clear mode."
