Do they really listen to or record all of the calls?
The amount of energy that is put into this does vary from facility to facility. All calls are recorded and can be made available for review by the prison or other officials. In general, not all calls are actually listening to, but that does not mean that someone is not listening or that they may not listen later on.
Also, because of their living environment, most of our loved ones can pick up on hints or subtle comments.