In 1966 my dad was serving as a missionary. At the time his zone leaders called every morning between 6:00 and 6:30 AM.
One day my dad got an idea for a reverse prank call. He called the information line that told the time every 15 seconds, and he tape-recorded the call from 5:55 to 6:30.
One morning, every time the phone rang my dad picked it up, put the receiver by his tape recorder, and played back a recording of the information line telling the time. As I said, he did this every time the phone rang.
The zone leaders couldn't understand why they kept getting the information line, so they called the telephone company. This was way back before there was anything digital about telecommunication, and telephone relays were racks of switches. The telephone company looked into the issue and they were absolutely baffled as to why they got the information line every time they called this one phone number.