Running out of numbers

Toronto will become Canada’s first city to have 3 area codes beginning in March 2013 with the introduction of 437, joining 416 and 647. The CRTC is already planning for the next number exhaust – it has set aside area code 387 as the next block of numbers, once Toronto runs short of the nearly 24 million numbers that can be assigned from the first 3 area codes.

Assigning an area code is an interesting art. In the olden days of rotary dial, the “best” area codes were the ones with the smallest number of pulses. In those days, area codes had a one or zero as the middle of the 3 digits, and the other two digits were anything but a one or zero. So, the most desirable area code was 212 and New York, the most populous region was given that assignment. The next best were 213 and 312, assigned to Los Angeles and Chicago.

It wasn’t about favouritism as much as the assignments considered the amount of time involved in dialing and transmitting the digits at a rate of 10 pulses per second. A zero took a full second for the 10 clicks; the digit 2 was sent in one fifth the time.

You can tell a lot about regional population densities in the mid twentieth century based on which area codes were assigned. Northern Ontario’s 807 and Newfoundland’s 709 were among the longest codes assigned.

Digital processors have enabled fully interchangeable area codes and central office codes, dramatically increasing the available pool of numbers. Still, there are some important considerations in choosing an area code. For example, the CRTC notes:

The Commission considers that it is a good assignment practice to use an area code that has not been used as a central office (CO) code within the area to be served, or in areas adjacent to it, because this reduces the potential for customer confusion when dialing. Since area codes 437 and 387 both meet this criterion, the Commission determines that area code 437 is to be used for current area code relief and that area code 387, for planning purposes, is to be set aside as the most suitable area code for future area code relief in Toronto, Ontario.

Toronto, a city of just over 3 million people, will have 24 million phone numbers available for assignment, plus another 24 million numbers serving the suburbs and Niagara region with area codes 905, 289 and the soon to be assigned 365 code. A major driver for consumption of numbers has been the introduction of competition. Generally, each competitive service provider in each exchange is assigned numbers on blocks of 10,000.

The North American Numbering Plan is one of the key areas of telecommunications administrivia that is important, but frequently goes without celebration. A hat tip to those numbering planners and those working on next generation routing schemes for more efficient assignment practices.