Editing Overlay complex (section)

==Number pool management==
The persistent unpopularity of new area code creation by splits or overlays has contributed to a change in the rules of number block allocation to conserve the pool of available telephone numbers. The change, which allowed for the assignment of smaller number blocks, is commonly known as [[telephone number pooling]], and has slowed the need for new area codes. For example, the western half of Washington, including Seattle, narrowly avoided the need for an overlay in 2001. [[Area code 564]], originally planned for introduction in October 2001, was delayed indefinitely in August 2001 after state regulators determined that the use of number pooling had resulted in more efficiency in the use of telephone numbers in western Washington. The 564 overlay complex was delayed until 2017.

Number pooling is not practiced in Canada. 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. Larger cities, particularly "megacities" that were created by amalgamations in the 1990s and early 2000s, have multiple rate centers, which were not combined for years, if at all. For example, [[Mississauga]], Canada's sixth-largest city, is split between five rate centers even though it has been a single municipality since 1974. [[Hamilton, Ontario|Hamilton]], the nation's tenth-largest city, is split between nine rate centers. [[Surrey, British Columbia|Surrey]], the nation's twelfth-largest city, is split between three rate centers and part of a fourth, while Ottawa is split between 11. Overlays became the preferred relief solution in Canada, partly because it is not possible to reassign a number from a smaller rate center to a larger one, even if the smaller rate center has enough numbers to serve it. By 2013, as mentioned above, seven-digit dialling had been eliminated in all eight{{disputed-inline|date=March 2023}} of Canada's original numbering plan areas.