There is however a "slight delay on the beta" for US PS3 gamers. It was meant to be available on PSN today but has now slipped until tomorrow.
The beta is stored under the PS Store's 'Latest'. It includes a single map, MP05 Frozen Dam. All game types from the full retail of Killzone 3 are available to be sampled: Team Deathmatch, 16-player Guerrilla Warfare, 24-player Warzone, 16-player Operations.
There's also Botzone which is for offline practice with 15 AIs. As long as you have a PSN account you can be a part of the Killzone 3 open multiplayer beta. "Unfortunately, we’re here to report that we will have a slight delay on the beta availability,” SCEA.
“The open beta was originally set to begin on Wednesday, February 2nd, but will now be available on Thursday, February 3rd at 10.00 AM Pacific Standard Time.” Sorry American PS3 gamers but you need to be patient just a little longer.
Killzone 3 releases exclusively for PS3 February 25th in Europe.