Sony has announced, via the PlayStation Blog, that gamers in the United States will be able to gain access to the SOCOM 4 Multiplayer Beta by simply purchasing a specially marked copy of Killzone 3.
This only applies to people in the United States though, as gamers in Europe will have to go through a slightly different route to get access to the beta.
According to a Tweet by PlayStation Europe, it will only be available to those who have bought in to PlayStation Plus - Sony's paid-for online scheme.
Killzone 3, for you Americans out there, will launch on the 22nd of February, exclusively on PlayStation 3.
Source: PlayStation Blog