I am well aware of the whole one-party/two-party consent laws and what
states they apply to.  However, I was wondering if it is only
recording that is illegal or if another person can listen in without
recording(Assuming both people on one end consent and it is a two
party consent state. So, second party does not know a second person is
listening)?

To make this a little more interesting, what if a person calls a phone
where a computer answers, and the computers calls a number you tell it
and talks to them while you listen in. Nothing is being recorded and
the computer was told to dial that number from the original person. 
Does a computer that talks and doesn't record even count as a "party"?