Yep and why I said put both in your box you build to block sound and signal. If I jam the phones it's gonna jam everything near by also. BTW is not a good idea. Maybe for a short time you could get away with it. LOLYou need to block out both ends of the conversation that includes both phones. Could be the other end of the line has a federal agent on it.
But think about it if we are doing a transaction that is breaking the law and you gonna have the govt after yea might as well have fun doing it.