What's to stop the overlord from having one of their underlings pass messages on their behalf, or even to pick a random "trusted" (as far as personal phone usag

What's to stop the overlord from having one of their underlings pass messages on their behalf, or even to pick a random "trusted" (as far as personal phone usage goes) prisoner in the yard and threaten to have them beaten (or killed, or raped) if they don't act as a communications mule? Give the prisoners communication with their family/friends, sure, but make it supervised personal visitation or actively monitored (also recorded and if necessary censored) phone calls, not mobile phones. Prisons only work because of force AND information asymmetry between the guards and the inmates, so allowing unsupervised personal communications is actively dangerous and counterproductive. It's not just organising crime outside outside of the prison or arranging the import of drugs and luxury goods, it's also the dangers of planning a riot, plotting an escape attempt, organising attacks on guards or rival prison gangs, and so on.