My first job out of college, the music on hold for our small office was provided by a boombox in the server/phone room tuned to the local soft-rock station. I recall the line-in was mono, so the cord was modified to use just one channel. You could also press a button on any desk set to listen to that music through the tinny speaker if you wished.
Anyway, one of the customer service guys wanted to listen to a World Series game during the work day, but the middle of the office had really poor radio reception. So he tuned the boombox to a local sports-talk AM station that was broadcasting the game, and listened through his desktop phone. And proceeded to forget about it once the game was over.
This went unnoticed, until a few weeks later when the company president was traveling, and called into the office. He was put on hold while transferred and promptly received an earful of shouty sports-radio idiocy.