Telephone number patterns prior to standardization
(ordered by type of pattern)



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 they are grouped by pattern type) and the companion page (on which the cities are arranged alphabetically, with the patterns for each city given) are provided.

On this page, the most important cities are listed by pattern type. (Each type is defined in the header for that group.) 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. Within each pattern type group, the cities are listed alphabetically.

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

  • The method of standardization (see the list of methods used on the alphabetically-listed companion page), and
  • The date of the change.

  • 3L-4N : Three letters beginning a word, followed by the four digits of the line number
    Boston, Mass. Mostly preserving the third digit,
    some altering the third digit
    Chicago, Ill. Mostly preserving the third digit,
    some altering the third digit
    September 18, 1948
    New York City Mostly preserving the third digit,
    some altering the third digit
    December 1930
    Philadelphia, Pa. (Bell) Mostly altering the third digit,
    some preserving the third digit
    July 5, 1946
    2L-4N: Two letters beginning a word, followed by the four digits of the line number
    Atlanta, Ga. Adopting a new name August 21, 1955-November 18, 1956 (phased)
    Baltimore, Md. Getting third digit from name
    Buffalo, N. Y. Adopting a new name
    (selected letters only, no word)
    Cincinnati, Ohio Inserting a random third digit 1955
    Cleveland, Ohio Inserting a random third digit
    Columbus, Ohio Adopting a new name
    Los Angeles, California Unknown, probably Inserting a random third digit
    Montreal, Quebec (Canada) Some exchanges: Inserting a random third digit;

    other exchanges: Adopting a new name

    January 1951-March 16, 1958 (phased)
    New Orleans, La. Adopting a new name 1955-1960 (phased)
    Omaha, Neb. Changed directly to ANC with no carrying over of exchange
    Pittsburgh, Pennsylvania Inserting a random third digit August 13, 1949
    Portland, Ore. Prefixing a digit to make a new name September 5, 1955
    Providence, R. I. Inserting a random third digit
    San Francisco, California Inserting a random third digit
    St. Louis, Mo. Inserting a random third digit
    Seattle, Washington Some exchanges: Inserting a random third digit;

    other exchanges: Adopting a new name

    March 16, 1958
    Toronto, Ontario (Canada) Some exchanges: Inserting a random third digit;

    other exchanges: Adopting a new name

    January 1951-March 16, 1958 (phased)
    Washington, D. C. Getting third digit from name
    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
    Philadelphia, Pa. (Keystone) Discontinued service without standardization



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    Last modified September 12, 2015.



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