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.
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.
> Add to the mix the thick walls
Because thick walls do not intercept enough of the radio signal. This only works in really remote locations - but e.g. here in Munich there are a number of jails in the city area. If someone would employ a jammer there, the neighbours would protest and/or sue.
A quick search turned up [1] which reckons £300 million for installation and £800,000 per annum to maintain. Which seems a bit pricey.
That said, there was a plan to trial it this year, but I can't remember if that was pre- or post-brexit.
http://motherboard.vice.com/read/a-canadian-prison-was-spyin...
http://www.theglobeandmail.com/news/national/opp-launch-crim...
Oh sweet summer Canadian children.
Add to that that signal strength changes with weather, and you have two solutions: either lots of expensive equipment or lots of buffer land owned by the prison. Both are expensive.