Utah currently utilizes 3 area codes. When first established by AT&T and the Bell System in 1947, 801 covered the entire state of Utah. The most recently added was 385 in 2009 as an overlay to 801. Today, 801 is the most populated with an estimated 2.1 million of the state's 2.8 million residents.
Sources: North American Numbering Plan Administration (NANPA), telecom providers, and the U.S. Census Bureau.