By 1960, the Bell System offered modest sized dial PBXs for small installations. These usually had cordless consoles. Customers of course could still get manual cord switchboards for such sizes, such as the 555 or 551. Indeed, around 1970 Bell Labs developed a manual cordless switchboard to replace the 555.
Obviously a primary tradeoff is that inter-office calls could be dialed instead of requiring an attendant. This was particularly useful for off hour times when an operator wouldn't be on duty. However, the attendant was still required to process incoming calls and perhaps serve as a "gatekeeper" to control toll calls (as was common in those days).
Having seen numerous examples of both types of boards in service in small installations, I was wondering what factors caused the users to pick one over the other. Obviously the dial board cost more to rent. Did the rent save the cost of an operator? As mentioned, an operator was still required to handle incoming calls. (If anyone knows of actual rentals for say a 555 or 551 vs a small dial PBX, could you share them with us.)
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