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:
| 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 | ,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) | |
| 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 | ||
| 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 | ||
| St. Louis, Mo. | Inserting a random third digit | ||
| 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 November 7, 2011.
