I did an experiment with creating "party lines" on the air with the callers. I think, in the end, it made for really terrible radio (sometimes experiments fail, and you move on!) but the callers were CRAZY for the party lines. Mostly they happened off air in the later days.
In fact, I recall that after my show ended at 7AM, I'd leave all the party lines going on the station's three office phone lines and usually fall asleep in the "listening room." (A room at the station with an old couch and a stereo). People would continue to chat on the party lines well into late morning, sometimes cut off when a staffer came in and picked up the phone to see who was on the line!
Hans, Gilly, Alzheimer's Al... so many other regulars are here! In one episode I know some old lady got onto one of the lines (dunno how, it was a minor technical challenge to accomplish for a caller) and the others on the line were mocking her. Those were crazy times.