On the official Playstation Blog, developer Zipper Interactive has shared some details about the Socom 4-beta. A private version will start up on March 15 and a week later Playstation Plus members will be able to join in on the shooting. A week after that, on March 29, everyone that bought Killzone 3 will get access, and on April 5 it will open up for the general public.
Two weeks after that, on April 19, the game is supposed to hit the retail shelves.