Southwestern Bell Telephone Company facility, Tulsa, OK. In the late they began to replace these huge switch banks with the first computer operated switching. "All those racks contained mechanical rotary switches. Made quite a racket.
December 1983 was the end of The Bell System. Founded in 1876 by Alexander Graham Bell, it ended after a federal judgement that American Telephone and Telegraph had to divest itself of their twenty two operating companies.