Telephone sets and apparatus were developed that allowed multiple lines to be answered on a single telephone set.PBXor private branch exchangeis a term that refers to any type of telephone switch that is located on the customer premises and provides service between telephones inside a single building or internal to a school, factory, or office.
In 1955, a specially designed answering service switchboard, called the 557, was developed.
This switchboard had the same modular construction first used with the 555 and 556 switchboards introduced in 1948.
To reduce the facility requirements of these answering service locations, a Secretarial Concentrator/Identifier system was installed.
This device would accommodate 100 transferred lines over six facilities.
This was the first PBX system that did not require an attendant to direct calls.
Each telephone used with the 750 PBX had five buttons on the base.
The 756 was also the first PBX to use the new wire-springthese provided redundant paths for critical circuits, which made the 756 far more reliable than older PBXs.
The 756 was also relatively compact and much quieter than the older step-by-step PBXs. For the first time, a dial PBX did not need to be installed in a special equipment room.
We have a Concentrator/Identifier connected to this board.