I've been told by someone who'd been in jail a lot, that attorney-client privilege is a huge loophole in the prison smuggling economy and someone in prison asking if you know "a good lawyer" is asking for a lawyer who would be willing to smuggle in contraband during privileged meetings.
Cellphones are always interesting because of the weird game of "sorta legal cellphone jamming" with managed access systems.
Can't just jam the phones, but you can set up a carrier-blessed sorta-Stingray that traps 'rejected' phones into a sinkhole network while bounces 'authorized' phones out to macro networks. It's kinda funky and wild.