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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. This made central office codes interchangeable. An interchangeable NPA code and an interchangeable central office code is a code that permits any of the ten numerals in the middle ...
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.
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 ...
The North American Numbering Plan is based on a ten-digit telephone number assigned to each telephone in the telephone network. The number is composed of the three-digit numbering plan area code, a three-digit central office code, and a four-digit station or line number. Certain rules govern the numerical format of each part.
The new area code's official in-service date was November 20, 2012, when new central office codes could be activated. A six-month permissive dialing period was conducted from April 21 to October 20 during which calls could be initiated by seven- or ten-digit dialing. Ten-digit dialing also required the prefix digit 1 (1+10-digit dialing). [7]
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.
This required 82 area codes to switch to mandatory ten-digit dialing by October 24, 2021, because they had already used 988 as a central office code. [3] Similar transitions are scheduled in most parts of the remaining single-code areas in Canada by May 31, 2023, due in part to the rollout of 9-8-8 service in that country. [4]
California (Stockton, Modesto, Merced, Tracy, San Andreas, and a part of central California extending into central Yosemite National Park) 1958: split of 916; 1998: split to create 559; 2022: overlaid by 350; 210: Texas (San Antonio metropolitan area) 1992: split of 512; 1997: split three ways to create 830 and 956; 2017: overlaid by 726; 211