Here's the lowdown about the SOCOM 4 beta codes, as explained by Zipper Interactive's Chris Roper:

To get early access to the beta, look for the SOCOM 4 callout on the front of all eligible copies of Killzone 3 (including both the standalone and Helghast Editions). Inside the box you'll find a PSN code that you'll be able to redeem for your early access as soon as the beta goes live. To find out when the SOCOM 4 multiplayer beta begins, be sure to check back at SOCOM.com once you pick up your copy of Killzone 3, hitting shelves on February 22nd.

Killzone 3 hits the PlayStation 3 exclusively on February 22.