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Area codes for Ottawa and Eastern Ontario
Area codes 613, 343, and 753 are telephone area codes in the North American Numbering Plan (NANP) for Ottawa and surrounding Eastern Ontario, Canada. Area code 613 is one of the 86 original North American area codes assigned in October 1947. Area code 343 was assigned to the numbering plan area in an overlay plan activated on May 17, 2010. Area code 753 was assigned as an additional overlay code for the numbering plan area, activated on March 26, 2022.

Area code 613 was originally assigned to a numbering plan area that included all of Ontario with the exception of the Golden Horseshoe, which was assigned the area code 416. The numbering plan area has been split twice. In 1953, the southwestern Ontario portion of 613 was combined with the western portion of 416 to become numbering plan area 519. In 1957, the vast northwestern portion of 613 was combined with the northern portion of 519 to receive area code 705. Since 1957, 613 covers only eastern Ontario, an area extending from Brighton and Deep River eastward to Saint Regis, Quebec. Ottawa and its twin city in Quebec, Gatineau, fall on the boundary between 613 and Quebec's area code 819. However, Ottawa shares a local calling area with the former city of Hull, Quebec (now part of the city of Gatineau). As a result, for 46 years, a call could be completed between Ottawa and Hull with only seven digits. While there are fewer than two million people in the geographic area served by 613, the bulk of that population lives in the Ottawa area. To preserve seven digit dialling between Ottawa and Hull, an exchange code protection scheme was implemented so that the same seven digit local number could not be assigned on both sides of the National Capital Region. Technically, it was only necessary that no two prefixes within the same local calling area be duplicates, but the code protection as implemented reserved the numbers across both area codes. This meant that if a 819 number was being used in Hull, the corresponding 613 number could not be used anywhere in eastern Ontario, even in areas a safe distance from the National Capital Region such as Brighton. Similarly, if a 613 number was being used in Ottawa–Carleton, the corresponding 819 number could not be used anywhere in western Quebec. Federal government offices in Hull duplicated their entire allocation of multiple exchanges worth of numbers available in 613 as part of a "dual dialability" scheme. By the turn of the century, both 613 and 819 were close to exhaustion due to Canada's inefficient number allocation system. Every competitive local exchange carrier received blocks of 10,000 numbers (corresponding to a single prefix) in every rate centre in which it planned to offer local service, no matter how small. A tiny unincorporated village (like Odessa, Ontario, with no telephone central office but still listed as a rate centre) usually received multiple 10,000 number blocks. Once a number is assigned to a rate centre and CLEC, it is unavailable for use elsewhere, even in cases when a rate centre has more numbers than it needs. Larger municipalities have multiple rate centres and multiple competing carriers in each. For instance, even though Ottawa has been a single municipality since merging with the Regional Municipality of Ottawa–Carleton in 2001, it still has 11 rate centres (plus portions of other rate centres primarily located beyond the city limits) – most with very similar local calling areas – which have never been amalgamated. The "Ottawa–Hull" exchange only covers the area that was the city of Ottawa prior to the 2001 amalgamation, plus the former suburbs of Nepean (central part) and Vanier and small sections of other urban communities. Since Canada does not use number pooling as a relief measure, many telephone numbers of the area code remained unused. The proliferation of cell phones and pagers, particularly in the larger cities in the 613 area (Ottawa, Kingston, Belleville, etc.) only magnified the problem. By 2006, the only remaining unassigned exchange prefixes in the entire 819 region were numbers which could not be assigned to the Quebec side of the Ottawa–Hull area without breaking seven digit dialling between Hull and Ottawa. Ten digit dialling in 613 and 819 became mandatory on October 21, 2006. Intraprovincial calls from rate centres with no local calling beyond a small fragment of their own area code were returning intercept messages if dialled as seven digits. Exchange protection in the National Capital Region was ended, except for the "dual dialability" scheme for government numbers on both sides of the river. This situation could have been avoided had some 1 613 versions of seven digit Ottawa Hull numbers been assigned to areas a safe distance from the National Capital Region years earlier. Within two years, it became apparent that a new area code was necessary due to the continued number allocation problem – an issue exacerbated by the proliferation of cell phones and pagers. A geographic split was quickly ruled out. Local telephone companies did not want the expense and burden of changing existing customers' numbers, which would have required en masse reprogramming of cell phones. As a result, overlay area codes were proposed for both 613 and 819. Area code 343, an overlay proposed in 2007, and approved by the Canadian Radio television and Telecommunications Commission on September 10, 2008, was activated for the region on May 17, 2010, several years earlier than originally anticipated. On 10 November 2021, the Canadian Numbering Administrator approved an additional overlay code for the numbering plan area 613/343. Area code 753 was assigned for activation on March 26, 2022.

The main incumbent local exchange carrier in area code 613 is Bell Canada, but there are some five independent companies serving rural exchanges: the Lansdowne Rural Telephone Company, serving Lansdowne; the North Frontenac Telephone Company, serving Sharbot Lake and Parham; the North Renfrew Telephone Company, serving Beachburg, Westmeath, and the area outside Pembroke; the Roxborough Telephone Company, serving Moose Creek; and the Westport Telephone Company, serving Westport. Also served by area code 613 and Bell Canada is Saint Régis, Quebec. The exchange covers the Mohawk nation territory of Akwesasne, which straddles the Ontario–Québec–New York border. Calls from Saint Régis to Fort Covington, New York, are local although they cross an international border. In the west, Rapides des Joachims, Quebec, shares an exchange with the adjacent Rolphton, Ontario.