Telephone number patterns prior to standardization
(Alphabetical by city name)



In the United States (and generally in Canada as well), telephone numbers generally conformed, by the late 1950s, to a standard pattern: a name (of which the first two letters were dialed) and a single digit (the "office number" in the early 1930s directories of New York City, which was the first city to use this pattern, but the term "office number" does not seem to have become general), constituting the exchange, and four digits (the "line number") specifying the individual telephone subscriber. On this site, this will be designated the "standard pattern," and whenever that term is used, it should be understood that what is meant is an exchange consists of two letters (taken as beginning a word) and a digit, and a complete telephone number consists of the exchange plus four more digits.

Prior to standardization, however, when dial telephones were originally introduced, there were a number of different dialing patterns used across the United States and Canada (yet more were used elsewhere, but those will not be considered on this site), and to help straighten these out, this page (on which the cities are arranged alphabetically, with the patterns for each city given) and the companion page (on which they are grouped by pattern type) are provided.

On this page, the most important cities are listed alphabetically. If there is a list of exchanges in that city that has been prepared for the site, clicking on the city name will send you to that section. Generally, two sets of exchange names will be presented: the "early" list, covering the exchange names used prior to the adoption of the standard pattern, and the "late" list, covering the names used when the standard pattern was in use in that city. There are two exceptions: Buffalo, New York, and Omaha, Nebraska. In Buffalo, the standard pattern was only adopted in a "selected letter" form, where two letters which did not begin a word were chosen; in Omaha, not even this modified standard pattern was used: Omaha went directly from its older pattern to seven-digit all-number calling.

For each city, three things will be given here, when known:

  • The pattern type (see the list of types below the main table), linked to the listing of cities using that type on the companion page,
  • The method of standardization (see the list of methods used below the list of pattern types), and
  • The date of the change.

  • City Pattern type Method of standardization Date of the change
    Atlanta, Ga. 2L-4N Adopting a new name August 21, 1955-November 18, 1956 (phased)
    Boston, Mass. 3L-4N Mostly preserving the third digit,
    some altering the third digit
    Baltimore, Md. 2L-4N Getting third digit from name
    Buffalo, N. Y. 2L-4N Adopting a new name
    (selected letters only, no word)
    Chicago, Ill. 3L-4N Mostly preserving the third digit,
    some altering the third digit
    September 18, 1948
    Cincinnati, Ohio 2L-4N Inserting a random third digit 1955
    Cleveland, Ohio 2L-4N Inserting a random third digit
    Columbus, Ohio 2L-4N Adopting a new name
    Los Angeles, Calif. 2L-4N Unknown, probably Inserting a random third digit
    Montreal, Quebec (Canada) 2L-4N Some exchanges: Inserting a random third digit;

    other exchanges: Adopting a new name

    July 16, 1951-September 21, 1958 (phased)
    New Orleans, La. 2L-4N Adopting a new name 1955-1960 (phased)
    New York City 3L-4N Mostly preserving the third digit,
    some altering the third digit
    December 1930
    Omaha, Neb. 2L-4N Changed directly to ANC with no carrying over of exchange
    Philadelphia, Pa. (Bell) 3L-4N Mostly altering the third digit,
    some preserving the third digit
    July 5, 1946
    (Keystone) 1W-4N Discontinued service without standardization
    Pittsburgh, Pennsylvania 2L-4N Inserting a random third digit
    Portland, Ore. 2L-4N Prefixing a digit to make a new name September 5, 1955
    Providence, R. I. 2L-4N Inserting a random third digit
    San Francisco, California 2L-4N Inserting a random third digit
    St. Louis, Mo. 2L-4N Inserting a random third digit
    Seattle, Washington 2L-4N Some exchanges: Inserting a random third digit;

    other exchanges: Adopting a new name

    March 16, 1958
    Toronto, Ontario (Canada) 2L-4N Some exchanges: Inserting a random third digit;

    other exchanges: Adopting a new name

    January 1951-March 16, 1958 (phased)
    Washington, D. C. 2L-4N Getting third digit from name

    List of pattern types
    3L-4N Three letters beginning a word, followed by the four digits of the line number
    2L-4N Two letters beginning a word, followed by the four digits of the line number
    1L-4N One letter beginning a word, followed by the four digits of the line number
    1W-4N A word (not dialed by a first letter, but rather with the names on the dial) followed by the four digits of the line number

    List of methods of standardization
    Preserving the third digit Change the third letter of a 3L-4N exchange to the corresponding digit, preserving the dialed number
    Altering the third digit Change the third letter of a 3L-4N exchange to a "random" digit, altering the dialed number
    Getting third digit from name Insert a third digit in a 2L-4N exchange corresponding to the third letter of the exchange name, as if it had been a 3L-4N exchange and the third digit were preserved
    Inserting a random third digit Insert a randomly chosen third digit in a 2L-4N exchange (sometimes nearly always the same digit in the whole city, other times truly random)
    Adopting a new name Adopt a totally new name and office number (often with the same name being used for what had been several different exchange names in 2L-4N days)
    Prefixing a digit to make a new name Insert a digit before the old 6; this requires adoption of a totally new name because the first two digits are the ones taken to make a name



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    Last modified September 12, 2015.



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