My 8 year old daughter drew the phone for this image.
Before there was caller identification it was pretty harmless to make prank calls.
When I was maybe 10 years old or so I remember doing a few random dials and asking "Is your refrigerator running?". The person would answer "Yes". Then I would (through muffled giggles) burst out "THEN GO CHASE IT!" and hang up and literally roll on the floor laughing. My favourite call was when I heard the person on the other end start to chuckle as I hung up.
It was completely innocent and fun and I'm sure something that would not work out quite the same today.