Area code 514 was one of the 86 original North American Numbering Plan Areas defined in 1947. It originally covered the western half of the province, from the American border to the Hudson Strait. This area nominally included several areas in the far northern portion of the province that still didn't have telephone service. However, in 1957, it was reduced to the region surrounding Montreal in a three-way split. Area code 819 was created out of the western half of the original 514 territory, while the far northern portion was added to area code 418. The final boundary change occurred in 1998 when the off-island suburbs became area code 450, which now completely surrounds 514.
This was intended as a long-term solution, but within less than a decade 514 was close to exhaustion once again due to Montreal's rapid growth and Canada's inefficient system of number allocation. Unlike the United States, Canada does not use number pooling as a relief measure. The allocation problem was exacerbated by the proliferation of cell phones. To solve the problem, 514 was overlaid with area code 438 beginning on November 4, 2006, making ten-digit dialing mandatory in the Montreal area.
Area code 438 was considered for overlaying 450 as well, but a later decision determined that 579 would be the overlay code for that area.