As of 2001, 94.1% of Idaho's occupied housing units had telephones. Idaho's first radio station, built by a Boise high school teacher and his students, began transmitting in 1921, was licensed in 1922, and six years later was sold and given the initials KIDO—the same call letters later assigned to Idaho's first permanent television station, which began broadcasting in 1953 and subsequently became KTVB. As of 2003, the state had 44 major operating radio stations (9 AM, 65 FM), and 13 major television stations. Several large cable systems serviced the state in 2000; and a total of 21,563 Internet domain names were registered in the state in the same year.