If you wanted to call someone, you first pick up the receiver and listen. You might suddenly be eavesdropping on another person's call, and you might try to convince them to hang up right there in the call.
Teenagers would beg their parents to get them a second line so they could talk to their friends without getting interrupted.
On a more rare occasion, someone might have left the receiver off the hook. When you do that, it would make a terrible racket for a short while, then it would give up. So if you needed the phone, you'd pick up the receiver and nothing would happen. You had to go through the house to each phone and make sure it was hung up.
