An already-legal answer is to set up local cell phone “towers” on the prison grounds, having directional antennas so that the prison’s neighbors are not affected. The connection between this tower and the outside network can be censored or watched at will. I’d hate to be a guard and find it impossible to use a cell phone in an emergency.
An already-legal answer is to set up local cell phone “towers”_Jim shakes head ... OVERKILL Red Neck, besides, you won't be able to contain the RF strictly to the 'grounds'.
Recommend instead a 'leaky radiating coax system' around the periphery of the building fed by a broadband mult-carrier or white noise source on the uplink frequency so the subscriber/prioner phone doesn't ever see/find the downlink signal ...