I could not imagine cell phone jammers would be מותר, but perhaps my gut-feeling is wrong...
Either way, I would be interested in knowing how they fit into halacha, and what the reasons behind forbidding [or permitting] their use would be. I would expect an answer to both cover the angle of how it affects an innocent user of a cellphone walking by, as well as the effect on the phone companies themselves.
Also of importance: would the location of the jammer (ie. whether in public or private domain) have an effect on the halacha?
I am specifically asking with regards to Jewish law, and without considering that they are in fact illegal by secular law (at least in the US).