In 1954, area code 402 was split. Eastern Nebraska retained 402, and area code 308 was assigned to western Nebraska. The overall roughly diagonal dividing line runs from the southeast between Hastings and Minden north into the northern part of the state and then west towards the eastern edge of the Sandhills in the northwest of the state.
Nebraska's most-populous cities, Omaha and Lincoln, are near each other in the eastern part of the state. In comparable circumstances in Kansas, where its most-populous cities, Wichita, Topeka, and Kansas City are in that state's eastern part, a north-south split was implemented placing Wichita in one area code, with Topeka and Kansas City in another. However, in Nebraska an east-west split was implemented in which Omaha and Lincoln retained 402, while Grand Island, then the state's third-most-populous city, was placed in 308.
Omaha and Lincoln are not only home to most of Nebraska's landlines, but also to most of its cell phones and pagers. As a result, area code 402 was nearly exhausted by the end of the 1990s. It was originally projected to be exhausted in 2001, but number pooling was implemented to stave off exhaustion. In 2009, however, NeuStar projected that 402 would be exhausted in 2010.
In March 2011, area code 531 was implemented as an overlay to area code 402. Although the first central prefix in 531 was not assigned until February 2013, ten-digit dialing has been mandatory for all calls from the 402 territory since spring 2011.