I don't think jamming would really be reasonable in a building. If the walls can contain the jamming signal to their building then the walls will keep out the original signal anyways. I think just RF blocking paint would be a more reasonable solution but this would also interfere with any radios in use by the guards and wouldn't do anything for any prisoners that are outside during the day.
Having the cooperation of the cell service providers would be good, you could just have a small pico cell that tries to blackhole any phones in the building but if a prisoner can smuggle in a cell phone then they can probably smuggle in any other handheld radio as well.
Isn't really a thing. These paints realistically manage 30 dB attenuation at around 1 GHz, which sounds great as a percentage ("99.x% reduction!"), but isn't sufficient to actually deny cellular service. [Paint also normally doesn't cover things like windows etc. which pretty much nullifies them anyway]
You can in fact dump a phone into a fridge or freezer, which (at least here) have steel sheets all over them. Phones still get cellular service.
What you would need is screen plating and windows with RF screening meshes (and of course special window frames and so on). This is a) extremely expensive b) can manage >60 dB attenuation.
"You can in fact dump a phone into a fridge or freezer, which (at least here) have steel sheets all over them. Phones still get cellular service."
Not necessarily true. I used a fridge as a quick alternative to Faraday cage for device testing and it worked fine. It was an old, heavy fridge though, newer ones may contain more plastics and fail to shield properly.
Is there anything like a chop gun for conductive fibers? I know it wouldn't make some perfect faraday shield but a conductive epoxy like material and some ultra fine metal fibers sound like that should be decent at blocking RF and I think it would be reasonable enough to make a special chop gun for it. It would make application a ton cheaper, a lot faster, and it should still be reasonably effective.
Having the cooperation of the cell service providers would be good, you could just have a small pico cell that tries to blackhole any phones in the building but if a prisoner can smuggle in a cell phone then they can probably smuggle in any other handheld radio as well.