The following are links is to various advertising brochures from various manufactures for dial Private-Automatic-Exchanges.
They were generally intended for use as a separate private telephone system for use _within_ an organization. They were not interconnected with outside Bell Telephone lines. They were usually sold, not rented, and over the long run saved money, especially in large organizations that had their own maintenance staff.
Many school districts, transit companies, and industrial sites used them for internal communications.
All of the brochures are from the Telephone Collectors International Library,
Automatic Electric Company of Chicago--general brochure, 1952:
North Electric Company, of Galion, Ohio:
Stromberg-Carlson, Rochester, NY, 1960:
Kellogg Switchboard & Supply of Chicago.
Note on the last page there is a photo of the company's plant. In years past, many industrial companies proudly included such pictures in their advertising brochures.
As an aside, Kellogg was located at 6650 S. Cicero in Chicago. According to google-streetview, that site is now a Dunkin Donuts. So many industrial sites have been razed or abandoned.