The United States uses more than 325 area codes which are assigned to specific geographic areas and fifteen other area codes that are not assigned to a geographic area. A few states have only one area code such as Alaska, Delaware, Hawaii, Maine, Montana, New Hampshire, North Dakota, Rhode Island, South Dakota, Vermont, and Wyoming.The states using the most area codes are California which is currently using 36 area codes, Texas 27 area codes, Florida 18 area codes, and New York 19 area codes. Although area codes are not assigned based upon population the locations with greater populations have an increased demand for area codes.The non-geographic area codes utilized in the United States are 456, 500, 521, 522, 533, 544, 566, 577, 588, 700, 710, 800, 833, 844, 855, 866, 877, 888 and 900.While many United States locations are assigned a single area code others are within geographic overlays. In an overlay, the new area code has the same geographic boundary as the existing area code. Existing phone numbers and local calling scopes don't change, but 10-digit local dialing becomes necessary. Ten digit dialing is necessary because two different homes in the same geographic area can have the same seven digit phone number but each would have a different area code.Some United States area codes have been created as a result of a geographic split. A geographic split divides an area code into two or more areas with each area receiving its own area code. Although local calls from one area code into another require dialing 10 digits, the local calling range usually does not change. Read more about recent and upcoming area code changes In the United States the responsibility for area codes is shared by Federal and state authorities. The North American Numbering Plan Administrator (NANP) is responsible for the administration, assignment and management of area codes. The FCC has jurisdiction over the telephone number administration. The FCC gives states the authority to decide when and how to introduce new area codes. This state authority is typically administered by the various state utility commissions.