Telephone Exchange Names

Telephone Exchange Names

A telephone exchange name was a distinguishing and memorable name assigned to a telephone exchange in the early years of telecommunications. In a large city with a linked numbering scheme and many local exchanges, the exchange name identifed the local exchange (central office) in a multi-exchange area. Each local exchange (central office) could have a maximum of 10,000 subscriber lines identified by the last 4 digits of the number; most local exchanges would be smaller but a few locations in the centre of large cities like New York or London could have two or more local exchanges in the one building. The first two or three leading characters of the exchange name formed the first digits of the subscriber telephone number

When automatic dial service was introduced in telephone networks, the leading letters of the exchange names were mapped into digits for dialing. The use of letters on the dial with 3 letters above each digit from 2 to 9, so that the exchange (central office) name could be spelt out by the first 3 digits, was proposed by W. G. Blauvelt of AT&T in 1917.. The mapping was typically displayed directly on the telephone dial by grouping the mapped letters above or around each digit. Several systematic coding schemes for telephone numbers were deployed in varies communities, sometimes evolving over time as the subscriber base outgrew older telephone numbering plans. Widely used numbering plans were systems of using 2 letters from the exchange name plus 5 digits (designated as 2L-5N); or 3 letters from the exchange name plus 4 digits (designated as 3L-4N). For both the 3rd digit was part of the exchange name, not of the local exchange (4-digit) number.

Telephone directories or any other telephone number displays typically listed the telephone number showing the significant letters of the exchange name in bold capital letters, followed by the digits that identified the subscriber line. On the number display on a telephone, the exchange name was typically shown in full, but only the significant letters were capitalized, while the rest of the name was shown in lower case, or as small caps.

Telephone exchange names were slowly abandoned after the introduction of area codes in the United States and other similar all-number calling systems around the world, such as the British all-figure dialling.