TELECOM Digest Editor noted in a comment to Lisa Minter :
Does the prison phone system have the technical capability to
> restrict the called party's phone in that way? For example, I
> forward my phone somewhere, then you, in prison, call me as we
> agreed on. Or, you call me from the prison, I flash the hook and
> bring someone else on the line with me. The prison says in their
> literature that is impossible. Is it really? PAT]
It is, because the person who is assigned to monitor the telephone call will disconnect it when they hear this happening. Not a technological solution but an effective one.
--scott