In Short

AT&T is one of the four major wireless service providers in America and sells a wide array of BlackBerry devices. Recently, they secured a deal to acquire regional service provider Alltel following a failed bid on T-Mobile. AT&T has the BlackBerry Z10  and BlackBerry Q10 in stock. 

AT&T in its current iteration was founded in 1983 after an antitrust lawsuit broke up the original AT&T (founded in 1885 by Alexander Graham Bell) into multiple regional service providers.