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Telephone number pooling, thousands-block number pooling, or just number pooling, is a method of allocating telephony numbering space of the North American Numbering Plan in the United States. The method allocates telephone numbers in blocks of 1,000 consecutive numbers of a given central office code to telephony service providers.
The Bell System engineers expected that the first numbering plan areas to require more than the 640 possible central office codes would not occur before c. 1973. [3] The solution for expanding the numbering pool within an NPA was to remove the restriction posed by not using 0 and 1 in the middle position of central office codes.
For example, 234 235-5678 is a valid telephone number; with area code 234, central office prefix (exchange) 235, and line number 5678. The number 234 911-5678 is invalid, because the central office code must not be in the form N11. 314 159-2653 is invalid, because the office code must not begin with 1.
The limitations for the usable leading digits of central office codes, imposed by using common names for central office names, and their leading two characters as guides for customer dialing could no longer be maintained when opening new central offices. By 1962 it was forecast that in 1985 the number of telephones in the nation would equal its ...
Thus, NXX is a number from 200 through 999, while XXXX is a range from 0000 through 9999. The first three digits of a telephone number are the numbering plan area code (NPA code, or simply NPA). The next three, NXX, identify the central office and the last four digits are the line number of an individual office.
Central office code protection was once common in communities on provincial or state boundary lines. It has been declining in use as inefficient allocation of numbering resources to the growing number of competitive local exchange carriers has caused depletion of available number prefixes, often requiring ten-digit local calls and overlay plans ...
Meanwhile, several blocks away in downtown Washington, Musk has asserted significant influence at the Office of Personnel Management, with at least one other employee formerly with Human Capital.
2023: returned to the pool of area codes available for future area code relief; 457: Louisiana (Shreveport–Bossier City, Monroe, Alexandria, Fisher, Tallulah, and most of northern Louisiana) September 25, 2025 [3] to be overlaid on 318; previously a fictitious area code assigned to identify Naked DSL/Dry Loop and dedicated data lines in ...