As it turns out the premium service will be a one time fee for all expansions and weapon packs in the game. The service will launch in June a week before the apparently severely overpriced "Close Quarters" comes out. Armored Kill, End Game, and a fifth pack that is rumored to launch in March 2013 are the announced DLC for Battlefield 3. There should also be some camo bundles and a few more character specializations released too.
The rumors are starting to fly on Twitter that the Battlefield Premium will launch on June 4th to coincide with the double XP weekend for the PC.