Toronto will add 437 to its existing 416 and 647 at the end of next month, while 365 will join 905 and 289 in serving a region that stretches from just outside the city to the Golden Horseshoe.
The new codes will come into effect on March 25, pushing the country's tally to 29, up from the original nine established in 1947, said a spokesman for the agency that oversees Canada's phone numbers.
That total is expected to rise to 35 in the next few years, driven by population growth as well as the boom in wireless technology, said Glenn Pilley, director of the Canadian Numbering Administrator.
"You get more people and they get more cellphones and they have multiple numbers, it's definitely going to add to it," he said Wednesday.
Saskatchewan will be the next province to branch out, followed by British Columbia, Alberta and other parts of southwestern Ontario, he said.
Manitoba already gained a new prefix last November when it made the switch to 10-digit dialling.
He said the new codes are needed to accommodate the surge in cellphones and tablets, many of which take up more than one phone number.
That's because some apps — including those meant to bypass charges for texting or long-distance calling, or to communicate with other machines — are assigned their own phone number, he said.
"Generally, nobody ever sees them, including the people that have the number because it's done automatically," he said.
Dense urban areas such as Toronto are quicker to use up the roughly 7.5 million unique phone numbers contained in each code, Pilley said.
He said it's likely few people will notice the change, however — at least until they get a new phone or receive a call from a strange number.
"It's going to be for most people a non-event in that it won't affect them because their phone number stays the same, their long-distance calling area stays the same and they already dial 10 digits."
— With files from Bruce Laregina.