Editing Ten-digit dialing (section)

==Code exhaustion relief==
When the demand for telecommunication services in a numbering plan area threatens to exceed the capacity of telephone numbers of a single area code, the local public service agency and the Federal Communications Commission initiate relief measures to mitigate the exhaustion, and assure continued service with minimal customer impact in the affected areas.

===Area code split===
In an [[area code split]], the established practice of relief from 1947 to 1992, the affected numbering plan area is divided into suitable parts, most often two, and assigned a new area code to one of the areas, while maintaining the existing area code in the other. The area that retained the code was most commonly the denser-populated or geographically or historically more significant part. This freed the telephone numbers already issued in the new area for use in the existing, now smaller, numbering plan area. This practice preserved seven-digit dialing in all affected areas.

===Area code overlay===
By 1992, a new method of relief became available from the proliferation of [[electronic switching system]]s that were based on [[stored program control]] (SPC), which reduced the need for electromechanical extensions of the switching fabric. This made it possible to assign multiple area codes to a single numbering plan area. An [[area code overlay]] required additional technology in all affected switching systems to recognize the local area codes and select the appropriate routing for local calls, even within the wire center. This eliminated the possibility of maintaining seven-digit dialing, and required the dialing of ten digits for all calls.

Consumer groups and some state regulators, such as the Illinois Commerce Commission and Citizens Utility Board for northwest Chicago, and the NYS Public Service Commission in NYC, opposed the requirement with attempts at litigation.<ref>{{cite web|url=https://www.nytimes.com/2003/01/23/technology/the-10-or-11-digit-local-call-fosters-anxiety-and-shrugs.html|title=The 10- or 11-Digit Local Call Fosters Anxiety and Shrugs|date=2003-01-23|publisher=NY Times}}</ref><ref>{{cite web|url=https://www.chicagotribune.com/2001/07/25/days-are-numbered-for-7-digit-dialing/|title=Days are numbered for 7-digit dialing|work=Chicago Tribune}}</ref><ref>{{cite web|url=https://www.chicagotribune.com/2001/07/27/11-digit-dialing-due-for-everyone/|title=11-digit dialing due for everyone|work=Chicago Tribune}}</ref>
The added effort in remembering and dialing longer numbers was perceived as a disadvantage of [[overlay plan]]s, which were introduced to reduce the inconveniences associated with the traditional method of splitting an area. However, overlays have become the primary relief method and ten-digit dialing has become increasingly common in the U.S. and Canada.