Re: "while talking to an unnamed associate over a recorded prison telephone line"
Obviously thinking like a Brit..
Here for your pleasure are the Miranda rights. Emphasis is mine:
"You have the right to remain silent; ANYTHING you SAY CAN and WILL be used against you in a court of law".
Trying to claim calls are private while under arrest in America, lol.
American law is thus - "Arrest them, they will eventually say something to someone, and then we have them"