208 is the North American telephone area code for all of Idaho.Because of its small population, Idaho is among a declining number of North American jurisdictions with only one area code. It is also one of the few whole-state area codes split between multiple LATAs—Southern Idaho (centered in Boise and spilling into Nevada, Wyoming and Malheur County, Oregon) and Coeur d'Alene (spilling into Montana and Washington). Additionally, the Spokane, Washington LATA spills into central Idaho.In 2001, the Federal Communications Commission projected the 208 area code would be exhausted in 2003. Due to the multi-LATA structure of 208, several numbers in Montana's 406, Wyoming's 307, northern Nevada's 775, eastern Oregon's 541 and eastern Washington's 509 weren't available for use. The number shortage was exacerbated by the proliferation of cell phones and pagers, particularly in urban areas. However, in 2002 the IPUC was able to successfully delay a split by implementing number pooling in Boise; this was later applied in 2007 to the rest of Idaho to stave off projected exhaustion in 2010.This area code is expected to exhaust by 2018 and a second area code will be needed as the state's population grows closer to two million; 11 other states with single area codes all have populations of about a million each. By 2013, it was obvious that all conservation measures had been exhausted, and a statewide overlay was recommended.On November 2, 2015, the Idaho PUC approved the addition of area code 986 as a statewide overlay, starting September 5, 2017. This was done to spare Idahoans, particularly in rural areas, the expense and burden of having to change their numbers; any Idahoan who has the original area code can keep it. It will be the second statewide overlay, following the example of area codes 304 and 681 in West Virginia.

North American area code 541 covers the majority of Oregon in terms of surface area, except the northwest part of the state. Its service area includes the cities of Eugene, Springfield, Corvallis, Albany, Medford, Bend, Ashland, The Dalles, and Pendleton, as well as the coastal region from Lincoln County to the California border. It began its split from area code 503 on November 5, 1995, and finished June 30, 1996. It is overlaid with area code 458, effective February 10, 2010.

Area Code 785 was the result of a split from 913 on July 20, 1997. Area code 785 covers telephone exchanges in most of northern Kansas. It stretches from the Colorado state line on the west to the Missouri state line on the east, while excluding the Kansas City Metropolitan Area (913). The largest city (by population) covered by the area code is the state capital of Topeka.

Area code 858 is a California telephone area code that was split from area code 619 on June 12, 1999. It is located in San Diego County, California. It covers some northern suburbs of San Diego, California and the northern half of the city proper, including the areas of Del Mar, Poway, La Jolla, Pacific Beach, Clairemont and MCAS Miramar.The outer northern suburbs of San Diego and the mountainous areas to the east (such as Ramona, Santa Ysabel, Warner Springs and Julian) are serviced by area codes 442 and 760, which were a result of an earlier split (and overlay) of area code 619.According to CPUC, this area code will be unified with 619 into an overlay after 18 June 2018 in which 10-digit dialling will be mandatory, which will make 7-digit calling extinct. The overlay has been a cost-effective solution for every new area code since 2008.