According to a recent correspondence with an AT&T Premier customer, the AT&T version of the Samsung Galaxy S III will be coming on or before June 21st. Interestingly, the correspondence seems to line up with previous rumors that the phone would come to AT&T on June 18th. Even if it does hold out until June 21st, that would put it in line with both T-Mobile and Sprint. This date is over two weeks ahead of Verizon's supposed launch date of July 9th.

Source: DroidMatters