> I always wondered why these things weren't used in prisons.
> 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.
You're probably right about urban prisons. I always think of them as remote but there are plenty in places with very high signal strengths, which would create problems. Low-power pico-cells inside the prison walls could presumably be configured to not cause problems outside. But yes, RF planning is a nightmare and there would doubtless be problems.
> 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.