AT&T opened up its pre-order period for the Samsung Galaxy S III today.  The carrier is only selling the 16GB model Galaxy S III for $199, and it is available in white and blue.  For those who have pre-ordered the device from AT&T already, they have been greeted with a June 18 ship date. With this in mind, it is highly possible that AT&T will end up launching the Samsung Galaxy S III a couple of days before other carriers on June 18.  So far, Verizon’s pre-orders are not expected to ship until June 28 at the earliest, or July 6 as a safer bet.  Lastly, T-Mobile already revealed that June 21 is the launch date for its own Samsung Galaxy S III.