The client will provide early access to Killzone's Frozen Dam multiplayer level, playable across three game modes: Guerrilla Warfare, Warzone and Operations. The offline multiplayer Botzone component will also be available.

There are more details on the modes through here. From what we can tell this beta will be available to everyone and not just PlayStation Plus subscribers.

Update @ 18:39PM GMT: Just a heads up, this is all kicks off on February 2nd in the US. More details here.