Toronto, ON utilizes an area code overlay in which area codes 416 and 647 serve the same geographic area. Ten digit dialing (area code + seven digit number) is necessary because two different homes in the same geographic area can have the same seven digit phone number but each would have a different area code. The area code overlay was put into service in 2001 when area code 416 was overlaid with area code 647.
In addition to Toronto, ON area codes 416 and 647 serve the City of Toronto. The surrounding suburbs are served by area code 905.