When I was in college my mother would call the dorm room repeatedly and leave messages demanding I call her back. She was convinced I was screening the calls on an answering machine. She would leave messages like "I know you can hear me. Pick up the phone. Pick up the phone. PICK UP THE PHONE!"
The dorm phones had voicemail. Once the phone stopped ringing you heard NOTHING until you picked up the phone to listen to messages.
My freshman year roommate was not impressed with having to slog through multiple messages, sometimes a full voicemail box, because my mother had repeatedly called and left messages while I was at class. Apparently he didn't find out his father had been hospitalized with a back injury until his mother drove to the university to tell him in person because the voicemail was full of my mother's ranting demands I call her back!
Between one of my sisters and myself my mother had a child at that school for seven years. In all that time nobody was ever able to get her to understand how voicemail differed from an answering machine.
I took to calling her back as soon as I got her messages. Since I was a college student with an active social life this usually meant I called her at close to midnight. She'd ask what was wrong and I'd respond that since she left 12 messages while I was out for the day it MUST have been an emergency, so I called as soon as I got the messages. It took a few months, largely because she spent a lot of time convinced I was lying about when I got the messages, but eventually being woken up by her eldest son saying "Hey, I just got your messages, what's the emergency?" wore her down. By the end of my freshman year she only left multiple messages in one day if she forgot she'd already called me.