Canadians' voracious demand for new telephone numbers means a move to 12-digit dialling may be only a few years away.

Toronto began dialling 10 digits for local calls this month and this spring will also get a new area code, 647, to keep up with the demand for new numbers.

Vancouver and Montreal are also getting new area codes, with other Canadian cities to follow. And many other major urban centres in North America are now using 10-digit dialling for local calls. But when cities need a third area code, there may not be one available. ''The 10-digit number is a limited resource which is running out fast,'' said Eric B. Morson, an expert on the phone numbering system.

''People don't recognize the looming crisis that is right down the road,'' Mr. Morson said.

Park Davis, president of Ottawa's Canadian Numbering Administration Consortium Inc. -- which allocates phone numbers -- said there are 18 to 20 possible phone numbers for every man, woman and child in North America. Still, he said numbers are fast running out.

''It's conceivable that we may run out of area codes and numbers within six years,'' Mr. Davis said. ''There is a great deal of debate as to how long this resource will last. Some people say as early as six years, some say as late as 20 years.''

The phone number shortage comes as users of cellular phones, pagers, fax machine and Internet lines continue to suck up numbers at breakneck pace. New companies competing to provide phone service also tie up far more numbers than go into service.

In the past six years North America has assigned 143 new area codes. The North American Numbering Plan Administration -- which assigns new area codes -- warned in its 1999 Exhaust Study that with accelerated growth, North America's last three-digit area code will be in use by 2006. With moderate growth, the area code bank will be empty in 2007. Under pressure from phone companies, the group later toned down its prediction, saying the continent has area codes to last through 2012.

Ian Angus, a spokesman for the Toronto Telecom Alliance, which is implementing 10-digit dialling locally, agreed 10 digits won't be enough.

''There is an entire process underway on how do we expand the phone numbers,'' Mr. Angus said.

''The [U.S.] Federal Communications Commission and the Canadian Radio-television and Telecommunications Commission have both issued notices on this.''

Under a switch to a 12-digit system, a number would be added to both the area code and three-digit local prefix.

Compounding the drain on numbers is an explosion in smaller, faster and cheaper phones that no one could have predicted. For example, a consumer buys a cellphone with a card for $10 of air time. After using up $9 of the card, the user throws the handset in a drawer. That ties up the phone number for about six months, cellphone providers said, until the company gives out the number to someone else.