Back when you had three way on your lan lines (around 1991), a friend and I used to do this with IHOP and Waffle House. We had one guy tell the other guy “This is probably AT&T’s version of Candid Camera.”
We would call a business and some random person from the phone book and listening to them argue who called who was pretty funny.
The best was in the phone book, there would be residence listings that had Teen Line listed under it. Calling the main line and the teen line and the parent bitching at the kid “I told you to never use your phone to call within the house so I have to get up!” And the kid trying to argue that the parents called them.
Good stuff.
I guess I should mention it didn’t always work because some people had called I.D., but that was far and few between. That’s why we stuck to businesses mostly. They didn’t have caller I.D.