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 four area codes form an overlay numbering 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,[1] which became operational on March 25, 2013.[2][3] Area code 742 was added to the overlay on October 16, 2021.
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 519/226/548/382 overlay area in the west, 705/249/683 in the north, 613/343/753 in the east, and Western New York State's 716/624 area on the eastern prong of the Niagara Peninsula. The incumbent local exchange carrier is Bell Canada.