Lots of interesting stuff to be found on the Internet Archive. For example, there’s a 1927 AT&T training movie on how to use the new phones that had just come out with dials. It’s a silent movie, of course. For more about the Internet Archive, I strongly recommend this great talk by Brewster Kahle, its founder.
Update: Ironically, coming back 18 years later to update some of the links, I had to use the Internet Archive to find things again… including the AT&T movie, which was still on their site but not under quite the same URL!