Two new area codes are coming to the Greater Toronto Area next month, as demand for cellphones and other mobile devices surge, authorities say.

In Toronto, the 437 area code joins the existing 416 and 647 codes. And, for those in the surrounding areas that use 905 or 289 codes — including Whitby, Burlington and Mississauga — the 365 area code will be introduced.

Both come into effect starting March 25, 2013, the Telecommunications Alliance said in a release on Wednesday.

Those signing up for new phones may still be assigned the existing area codes for the next few months — at least until they run out of numbers.

Mobile devices boost demand for area codes

"These new area codes reflect the growing use of cellphones and other mobile devices," said Glenn Pilley, director of the Canadian Numbering Administrator, in a statement.

"Telecommunications service providers will be able to accommodate the growing demand for new telephone numbers with absolutely no impact on customers. We expect the first numbers with the new area codes to be assigned over the coming months as part of a seamless transition process."

Demand for numbers has increased due to population growth, as well as cellphone use, over the years.

The Canadian Radio-television and Telecommunications Commission announced in 2011 the area code 437 would be introduced within two years, as the current inventory of 416 and 647 numbers were being rapidly depleted. It also set aside the area code 387 for future use, but did not specify when.

The CRTC also said in 2010 that it would be adding the 365 area code for suburbs around the Toronto area as the demand for new numbers was gobbling up the available numbers. Without the new area code, it estimated that the region would run out by 2014.