Area codes 905, 289, 365, and 742 are telephone area codes in the North American Numbering Plan (NANP) for the Golden Horseshoe region that surrounds Lake Ontario in Southern Ontario, Canada. The numbering plan area (NPA) comprises (clockwise) the Niagara Peninsula, the city of Hamilton, the regional municipalities of Halton, Peel, York, Durham, and parts of Northumberland County, but excludes the City of Toronto.
The area codes form an overlay plan for the same geographic region, where area code 905 was established in October 1993 in an area code split from area code 416. When 289 was overlaid on June 9, 2001, all local calls required ten-digit dialing. On April 13, 2010, the Canadian Radio-television and Telecommunications Commission (CRTC) introduced another overlay code, area code 365, which became operational on March 25, 2013.
The numbering plan area surrounds the city of Toronto (area codes 416/647/437), leading locals to refer to the primarily suburban cities surrounding Toronto as "the 905" or "905 belt". It is bound by the 519/226/548 overlay area in the west, 705/249/683 in the north, 613/343 in the east, and New York State area code 716 on the eastern prong of the Niagara Peninsula. The incumbent local exchange carrier is Bell Canada.
Area code 905 was once assigned to Mexico City during the time when Mexico was expected to become a member of the North American Numbering Plan. However, Mexico established its own numbering plan within the country code designation of +52. The assignment of 905 was finally officially withdrawn by February 1, 1991.
By October 1991, area code 905 had been assigned to relieve exchanges in the Golden Horseshoe, which was and still is Canada's largest toll-free calling zone. The Golden Horseshoe's explosive growth in the second half of the 20th century and the corresponding expansion of telecommunications service would have made another area code necessary in any event. However, the timetable was advanced because Canada's system of number allocation does not use number pooling as a relief measure. Instead, each competitive local exchange carrier (CLEC) is assigned blocks of 10,000 numbers, which correspond to a single three-digit prefix, for every rate centre in which it plans to offer service. Most rate centres do not need that many numbers, but excess numbers cannot be reassigned elsewhere once they are assigned to a rate centre. The problem was not as severe in the Golden Horseshoe as in the rest of Canada since then as now, numbers tended to be used up fairly quickly. However, the number allocation system did not allow number blocks to be reassigned from smaller rate centres to the Toronto rate centre. The proliferation of cell phones, pagers, fax machines, and dial-up Internet connections made it obvious that the Golden Horseshoe needed another area code.
Automatic number identification (ANI) in some central office switching systems in the numbering plan area started operation on October 11, 1992. The new area code entered service on October 11, 1993. Permissive dialing of 416 continued across the Golden Horseshoe until January 1, 1994. However, portions of the 905 territory have remained ever since a local call to Toronto.
The creation of area code 905 was intended as a long-term solution. However, five years after its introduction, area code 905 was close to exhaustion far sooner than anticipated, again due to the proliferation of cell phones and pagers. By 1999, the CRTC had established an ad hoc committee to study code relief planning for area code 905. A split of the NPA was considered, with various options being presented:
The overlay option was chosen because it would cause the least disruption and was supported by all of the carriers. A split would have forced customers to change their numbers for the second time in less than a decade and forced the reassignment of cellphone numbers. For the same reason, Toronto was overlaid with area code 647 (and later 437).
The 289 NPA overlay was approved by the CRTC on August 15, 2000 in Order CRTC 2000–772. The order had the CRTC direct Bell Canada to implement a ten-digit local dialing plan. Area code 289 came into service on April 7, 2001, and it had come into full operation by June 9, 2001.
Area code 905 was officially exhausted in November 2005, just twelve years after its creation. All new central office prefixes were assigned with NPA 289. Part of the problem stemmed from the creation of single-tier megacities across Ontario at the turn of the millennium. Many of the enlarged cities are split between multiple rate centres, which have never been amalgamated. An example is Hamilton, Canada's tenth-largest city, which is split between nine rate centres. That applies also to newer cities, which were created prior to the introduction of the 905 code. For example, Mississauga, the largest city in the NPA, and the sixth-largest city in Canada, is split between five rate centres even though it has been a single municipality since 1974, but there is a single Mississauga listing in the phone book. Another example is Vaughan, which is split between three rate centres and part of a fourth even though it has been a single municipality since 1971. Unlike Mississauga, Vaughan is not even listed in the phone book, which lists the various rate centres separately.
The Golden Horseshoe's continued growth caused area code 365 to be assigned for further relief on March 25, 2013. Also, area code 742 was assigned on October 16, 2021.
A numbering plan exhaust analysis of 2020 projected an exhaust date of March 2023 for the numbering plan area.
The term the 905 or the 905 belt is used to describe the suburban areas of the Greater Toronto Area, while Toronto proper is referred to as the 416. The term 905er is often used pejoratively by Toronto residents to refer to suburban residents outside the city. Canadian rapper Maestro rendered homage to the area code in his song "416/905 (TO Party Anthem)"; "TO" (pronounced "T" "O") is an abbreviation or nickname locals use when referring to the city of Toronto. In June 2015, Maple Leaf Sports & Entertainment announced the formation of an NBA Development League team for the Toronto Raptors based in Mississauga called Raptors 905.
The term has been used in the context of Canadian politics, where the 416 is a stronghold of Liberals and NDP, whereas the 905 (excluding Hamilton) historically had strong ties to the Progressive Conservative Party. The region has, however, backed opposition parties as a protest vote, including both the NDP in the 1990 provincial election and the Liberals in the 2003 provincial election, as a backlash to the incumbent government. In both cases, the opposition party was elected to government with strong backing of the 905 region. The 2011 federal election saw the 905 region become predominately represented by candidates of the Conservative Party of Canada, while one third of the 416 ridings were won by Conservatives, many through vote splitting between the Liberals and NDP. In the 2019 federal election, the Liberals successfully held all 25 ridings in the 416, which they won in 2015. However, the parties were fighting over control over the 905 as historically, winning the 905 is key to parties forming government. In the end, most 905 ridings were won by the Liberals over the Conservatives. The Liberals ultimately beat the Conservatives and formed a minority government with the support of the 905.
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The area around Toronto is known colloquially as "the 905," after the area code that was added in 1993 and covers such areas as Mississauga and Niagara Falls.
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