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.
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.
The problem was not as severe in the Golden Horseshoe as in the rest of Canada since, numbers have tended to be used up fairly quickly.
The proliferation of cell phones, pagers, fax machines, and dial-up Internet connections made it obvious that the Golden Horseshoe needed another area code.
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.
The order had the CRTC direct Bell Canada to implement a ten-digit local dialing plan.
The Golden Horseshoe's continued growth caused area code 365 to be assigned for further relief on March 25, 2013.
[10] 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.
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.