Thus, only area code references, where present for long-distance calling, required updating in directories, letterheads, and business cards.
With the proliferation of electronic switching systems starting in the 1980s, it became possible to implement another method for expanding numbering plan resources, the area code overlay.
Most implementations of the overlay method have required ten-digit dialing, by including the area code, for all subscribers for all calling destinations, local or long-distance.
A similar practice was implemented on a large scale in the metropolitan area of Washington, DC, and its suburbs in Maryland and Virginia.
However, Canada's inefficient number allocation system and the proliferation of cellphones brought 819 to the brink of exhaustion by the turn of the century.
Although landline growth has sharply dropped and even decreased, largely by the elimination of residential landlines in favor of personal mobile phones, it has been replaced by the even worse problem of data-only devices (hotspots, modems, netbooks, and especially popular tablets), which still require a telephone number for use on cellular networks even if they are unable to make or receive regular calls.
Most overlay plans introduced the inconvenience of mandatory ten-digit dialing in which the area code must always be included even for local calls.
Ten-digit dialing is not a technically necessary requirement, and 917 was initially deployed without it, but a US Federal Communications Commission (FCC) mandate instituted it at the demand of major telephone companies, to whom an overlay is considered a disadvantage to competitors.
[2] In Canada, ten-digit dialing is also a requirement of the Canadian Radio-television and Telecommunications Commission in overlay area codes.
In many cases, such as 847 in Chicago's northwestern suburbs and 212 in New York City, an overlay was an additional disruption to a community that had already been subject to one or multiple code splits, encountering pushback from state regulators or consumer groups.
Connecticut, Illinois, Oregon, New Jersey, Massachusetts, Maryland, Pennsylvania, Texas, Virginia and, more recently, California have also implemented many overlays.
Telecommunications companies have increasingly favored overlays even in sparsely-populated rural areas in which ten-digit local numbers are unnecessary, as split plans force cellular providers to reprogram millions of client handsets.
Customers also incur costs to publish new letterheads and to reprogram stored address book data on individual devices.
[3] This is especially practiced for area codes that have been pushed back to the brink of exhaustion after being recently split, as carriers want to minimize additional customer inconveniences.
Within only five years, 410 was already on the brink of exhaustion due to Baltimore's rapid growth and the proliferation of cell phones, pagers, fax machines and dial-up Internet lines.
However, the area's dominant telephone provider, Bell Atlantic (now part of Verizon) realized that a split would have forced residents of either Baltimore or the Eastern Shore to change their numbers for the second time in the 1990s.
[citation needed] Additionally, a split would have forced half of Puerto Ricans to change telephone numbers for the second time in a decade.
West Virginia had been served by 304 since the inception of the North American Numbering Plan, but it was obvious by 2007 that the state needed a new area code.
The proliferation of cellphones, fax machines, pagers, and dial-up Internet connections, particularly in larger markets threatened central office code exhaustion in many areas.
Particularly severe allocation problems manifested themselves at the turn of the century in Metro Toronto and the Golden Horseshoe, the center of Canada's largest local calling area.
By 2023, seven-digit dialing had been effectively eliminated nationwide in Canada (as well as in most of the United States), due to both overlays and other regulatory requirements.
Every competing carrier is issued blocks of 10,000 numbers for every rate center in which it offers service, regardless of its actual subscriber count.
Individual rate centers exist even in the smallest hamlets, and even tiny unincorporated villages receive multiple blocks of 10,000 numbers.