Editing Seven-digit dialing (section)

==Timeline==
===Before 1947===
Local telephone numbers were governed by varying local numbering plans based on historical growth of services. Places without dial service often used special party line syntax (e.g., 2-R-48). The largest cities already used seven-digit telephone numbers and had dial service.

===1947 to 1951===
The [[American Telephone and Telegraph Company]] (AT&T) announced a nationwide numbering plan in 1947, which divided the United States and Canada into 86 numbering plan areas and assigned a unique area code to each. All area codes had a zero or one as the middle digit. A zero indicated that the state or province was served by a single area code, and a one indicated multiple divisions of a state or province.

Area codes were used as a universal destination routing code to the numbering plan area, and replaced the trunk routing codes that operators previously had to look up at the toll switching centers under the [[General Toll Switching Plan]] that was in use since 1929. In [[Operator Toll Dialing]], automated equipment translated area codes to routing information. Systematic conversion of city dial systems commenced to the seven-digit (two-letter-five-number) numbering plan. Central office codes were restricted to the digits ''2'' to ''9'' in the middle position, to facilitate machine recognition when an area code was dialed. The same rule already applied to the first digit for technical and historical reasons.

===1951 to 1960===
Direct Distance Dialing (DDD) trials were conducted by the end of 1951, in which subscribers in Englewood, New Jersey, could dial long-distance calls to a select group of remote destinations, as far away as San Francisco, by using an area code.

DDD technology expanded to other major cities, By 1960, it was available in a few places in Canada, as well as most large American cities. This decade is notable for implementation of some thirty more area codes, including in Alaska, Hawaii, and the Caribbean.

===1960 to 1981===
Major progress may be noted in provisioning DDD service. Long-distance billing was computerized in the 1960s to the early 1980s. Few area codes were introduced during this time. [[Toll-free telephone number|Toll-free]] 800-service was introduced. Service demands in the largest American cities of New York and greater Los Angeles area resulted in the first use of interchangeable central office codes (NXX). All-number calling was implemented, replacing 2L-5N telephone numbers. A very small number of places still did not use a seven-digit numbering plan by 1981.

===1981 to 1994===
New area code assignments were increasing in the 1980s. From 1990 to 1994, all remaining assignable codes entered service. The exhaustion of NXX codes necessitated interchangeable codes in several more area codes. Ten-digit dialing, or 1+10D, was implemented in area codes with interchangeable NXX codes. Protected dialing plans as in national capital areas were discontinued to help meet demand without area code relief. As 1994 neared its end, ten-digit dialing became required throughout the numbering plan in preparation for interchangeable NPA codes.

All local numbers now had seven-digit, as the last technological hold-outs had given way to modern switching technology. The concept of a ten-digit local number was conceived, as New York had an overlay code (917, implemented in 1992), but seven-digit dialing was still the norm.

===1995 to 2019===
Interchangeable NPA codes were introduced in Washington state and Alabama, and some forty new area codes were introduced in 1999 as relief was implemented for pent-up demand. This included two additional toll-free prefixes as the 888 code was quickly exhausted. Since 1999, a more steady rate of area code introductions has taken place, the rate being slower due to one or more factors:
*economic recession
*consumer resistance
*conservation measures or regulatory measures
*pent-up demand being satisfied
*new market entrants leaving the business.

With overlays in several areas (the relief method of choice in Canada since 2000), ten-digit local numbers were supplanting seven-digit dialing; by 2019, only four Canadian area codes ([[Area code 506|506]], [[Area code 709|709]], [[Area code 807|807]] and [[Area code 867|867]]) were still single-code areas (no overlay) and allowed seven-digit local dialing. Although fewer American area codes were overlaid, seven-digit dialing was also disappearing in the United States.

===2020 to present===
{{further|Ten-digit dialing#Ten-digit dialing in non-overlay areas}}

On July 16, 2020, the FCC adopted rules to establish 988 as the three-digit phone number for the [[National Suicide Prevention Lifeline]].<ref>{{Cite web|date=July 17, 2020|title=Designating 988 for the National Suicide Prevention Lifeline|url=https://www.fcc.gov/document/designating-988-national-suicide-prevention-lifeline-0|url-status=live|archive-url=https://web.archive.org/web/20200807163501/https://www.fcc.gov/document/designating-988-national-suicide-prevention-lifeline-0|archive-date=Aug 7, 2020|access-date=July 6, 2021|website=FCC.gov|publisher=[[Federal Communications Commission]]}}</ref> 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]].<ref>{{Cite web|title=Transition to 10-digit dialing for 988|url=https://www.nationalnanpa.com/transition_to_10_digit_dialing_for_988/|url-status=live|archive-url=https://web.archive.org/web/20210426180901/https://www.nationalnanpa.com/transition_to_10_digit_dialing_for_988/|archive-date=April 26, 2021|access-date=July 6, 2021|publisher=[[NANPA]]}}</ref>

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.<ref>{{cite web|url=https://crtc.gc.ca/eng/archive/2022/2022-234.htm|title=Telecom Regulatory Policy CRTC 2022-234: Introduction of 9-8-8 as the three-digit abbreviated dialing code for mental health crisis and suicide prevention services and Northwestel Inc.'s application for modified implementation of ten-digit local dialing|author=[[Canadian Radio-television and Telecommunications Commission]]|date=August 31, 2022|access-date=September 6, 2022}}</ref>