Telephone service went through radical changes during the 1950s. At the beginning of the decade, most households shared party lines with their neighbours, and telephone numbers consisted of the name of an exchange (the first two letters were dialled) followed by four numbers. By 1959, according to AT&T, more people had private lines, telephone numbers had grown to seven numbers with no letters and direct dialling that bypassed the operator had been introduced. Switchboards that served telephone customers and businesses also metamorphosed into more sophisticated mechanisms.
Answering Service Switchboard
Because some phone customers, such as medical doctors, had a need for 24-hour answering services and local telephone carriers could not provide them, private answering service businesses began cropping up in the 1950s. A special answering service switchboard, the 557A, was introduced in 1955. At the end of a working day, the doctor's office receptionist depressed a transfer key. While the key remained in the transfer position, incoming calls to the medical office were routed to the answering service's 557A switchboard. So that massive cable equipment would not be necessary, a concentrator/identifier system was installed that accommodated 100 transferred lines.
Automated Long Distance Switching
The dial tone was introduced during the 1950s, replacing the operator's "Number, please." Long-distance switching became automated at this time. This allowed a single operator to build the needed connection by dialling a sequence of routing codes to activate the electromechanical switch. Within a decade, dialled area codes would make this step obsolete. The No. 4 crossbar switchboard was first used by AT&T for automatic switching. The company modified it, producing the No. 4A model, when customer-dialled long-distance calls became possible.
Private Branch Exchange Systems
A private branch exchange, commonly known as a PBX, refers to multiple phone lines at a place of business that allow internal communications between employees. Up until the early 1950s, 20 lines were the maximum such a system could handle. Several new PBX models came out during the '50s, most with greater capacities than their predecessors. One popular system, the 756 switchboard, offered up to 60 lines although it was relatively compact, and proved to be more reliable and quieter than earlier models. Western Electric's 608 PBX switchboard was designed as a universal replacement for the switchboards that came before it. Able to serve up to 2,400 lines, it had a modular design that made replacement of defective parts easier. New materials, plastic and fibreglass, were used in its construction, instead of the traditional wood. Cordless PBX switchboards in the 507 series were introduced in 1952. Much smaller than a cord PBX, the cordless models took up less room on a receptionist's desk, but could only accommodate 12 lines. These first cordless units were only practical for small offices with light phone traffic.
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