Toronto's original manual telephone exchanges were recognized by an exchange name and a block of four-digit line numbers. The "GRover exchange" at Kingston Road and Main Street in
East Toronto became the first Canadian dial exchange in 1924. Montréal got its first dial telephones one year later. The numbers were dialled as two letters and four digits (2L+4N).
Grover 1234 was dialled GR-1234 (or 47-1234). Conversion to seven-digit (2L+5N) format began in 1951, and continued until the introduction of
direct distance dialling (DDD) in 1958. Area code 416 was one of the 86
original North American area codes, assigned by the
American Telephone and Telegraph Company (AT&T) for
Operator Toll Dialing in 1947. It comprised
Southern Ontario including the populous
Golden Horseshoe region in southern Ontario. Ontario and
Quebec were the only provinces to be assigned multiple area codes at the inception of the continental
telephone numbering plan. Area code 416 has been split twice. The first came in 1953, when its western portion (including Kitchener) was combined with the southern portion of area code 613 to form a new numbering plan area with
area code 519. This left 416 largely coextensive with the area that is generally recognized as the core of the
Golden Horseshoe. Despite rapid growth in the
Greater Toronto Area (GTA) in the second half of the 20th century, this configuration remained for 40 years. By the late 1980s, 416 approached exhaustion of available central office codes because of the GTA's continued growth. All
competing carriers are assigned 10,000-number blocks, which correspond roughly to a single prefix, in each
rate centre in which it plans to offer service, regardless of its actual subscriber count. The rapid growth in telecommunication services in the Greater Toronto Area in the 1990s, with the proliferation of cell phones, fax machines, and pagers, made it apparent that the Golden Horseshoe needed another area code. This resulted in a second split of 416 which took effect on October 2, 1993. The 416 numbering plan area was reduced to
Metro Toronto (
East York,
Etobicoke,
North York,
Toronto,
Scarborough, and
York), while the rest of the Golden Horseshoe (the
Niagara Peninsula, the regional municipalities of
Durham,
Halton,
Hamilton–Wentworth,
Peel, and
York, and parts of
Northumberland County) were assigned
area code 905.
Permissive dialing, during which dialing of either 416 or 905 was acceptable in a dialed number terminating in the new NPA, was effective until March 26, 1994. With the
amalgamation of Metro Toronto into the "megacity" of Toronto in 1998, 416 became the only Canadian area code to serve just one rate centre and just one city. Many of Canada's larger cities, especially "megacities" that have been created from mergers of previously separate cities (such as
Ottawa and
Hamilton), are split between multiple rate centres that have never been amalgamated. Toronto is an exception; it has been a single rate centre, by far Canada's largest, since 1977, with the merger of the historical Agincourt, Don Mills, Islington, New Toronto, Scarborough, West Hill, Weston, and Willowdale exchanges into the Toronto exchange. The 1993 split had been intended as a long-term solution for Canada's largest toll-free calling zone. Within five years, however, 416 was once again approaching exhaustion. Toronto's size and status as a single rate centre have caused numbers to tend to be used up fairly quickly. Therefore, the number allocation problem was not nearly as serious as in other Canadian cities that are split between multiple rate centres. Splitting Toronto between two area codes, a solution adopted in the United States for cities like
New York City,
Chicago and
Los Angeles, was ruled out because of the area's high population density and the lack of a suitable boundary along which to split. Another option was adding an
overlay area code to 416. Overlays were a new concept at the time, and were controversial because of the requirement for
ten-digit dialling. Despite this, Bell and other telephone companies pressed for an overlay since they wanted to spare customers the expense and burden of having to change telephone numbers, which would have required a massive reprogramming of cellular telephones. Ultimately, the decision was in favor of an overlay. On March 5, 2001, 416 was overlaid with area code 647, creating Canada's first overlay. The implementation of 647 made ten-digit dialling mandatory in Toronto. Within a decade, however, the continued proliferation of cell phones brought both 416 and 647 close to exhaustion once again. A new overlay area code, 437, started operation on March 25, 2013. That effectively allocates 24 million numbers to a city of 2.5 million people. Since the implementation of area code 647, overlays have become the preferred solution for exhaustion relief in Canada. Not only do they eliminate the need for renumbering existing subscriber accounts, but they are an easy workaround for the number allocation problem. As of April 28, 2023, all eight of Canada's original NPAs have been overlaid. Only three Canadian area codes (
709,
807, and
867) are still single-code areas, without overlay, still allowing
seven-digit dialing for local calls. A 2020 exhaust analysis by the NANPA projected exhaustion in 2025 for central office prefixes in the service area. In relief planning since 2023, area code 942 was activated for service in the numbering plan area on April 26, 2025, to provide new numbering resources.
Area code 387 has been reserved for future use in Toronto. ==Local calling area==