This drove me up the wall yesterday ...
I got a call about a problem just as I was about to leave work. The solution required help from another employee, so I called him, asked him to do a task, and requested that he call me when he was done so that I could do my part from home. I then went to my car.
On the way home, my phone rang no fewer than twelve times. We're not allowed to use cell phones while driving where I live, so all I could do was helplessly listen to it ring. It would ring several times, stop (presumably when my colleague realized I wasn't going to answer), and then start ringing again two minutes later. I kept yelling at the phone (because I'm mature that way) "LEAVE A VOICEMAIL, FOR CRYING OUT LOUD!"
When I got home (about 20 minutes later), I called the guy back. He said in surprise "Oh, it's you! I was just about to leave you a voicemail." Oh, NOW you've suddenly discovered voicemail?