List of area code overlays
An area code overlay is a numbering plan area (NPA) in the North American Numbering Plan (NANP) that has multiple area codes assigned. Overlay complexes are used to add central office prefixes in an NPA to increase the number of available telephone numbers. See also
 List of North American Numbering Plan area codes
 List of future North American area codes
 Original North American area codes
 Telephone numbers in the Americas

References

North American Numbering Plan