Killzone: Mercenary's closed multiplayer beta is now live, so those of you who got in should already have the necessary information to get going. However, for those of you who missed out, Sony will be opening up multiplayer beta in "late August," with more details coming "really soon."
Sony notes that the multiplayer Beta voucher that was part of the promotion via PlayStation Home is for the Open Beta.
The closed beta, which will presumably also apply to the open beta, will "give gamers an early look into the power and promise of PS Vita as the optimal handheld platform for first-person shooters." While I had a chance to preview the game's multiplayer at an event earlier this year, the beta will likely go more in-depth than what I saw, showing off the "diverse range of weapons, grenades, armor, and special VAN-Guard devices."
[PS Blog]