High Quality Content by WIKIPEDIA articles! AT&T Corp., originally American Telephone and Telegraph Company, is an American telecommunications company that provides voice, video, data, and Internet telecommunications and professional services to businesses, consumers, and government agencies. During its long history, AT&T was at times the world`s largest telephone company, the world`s largest cable television operator, and a regulated monopoly. At its peak in the 1950s and 1960s, it employed one million people and its revenue was roughly $300 billion annually in 2006 dollars.