Bell System Film from the 1970's

Complete Record: The following is an interesting film that I obtained from a source that bought the assets of a film lab many years ago. It's a film that he called 'Bell Performance.' No beginning or ending titles, but still very interesting to me as Bell System nostalgia. We see telephones being created and stress tested and all kinds of other neat stuff. I'm not sure which of the Bell entities created this film - an Illinois Bell truck is seen in this film, but I don't know if they created it.