The bar for multiplayer FPSs on handhelds must be pretty low, but bless 'em, developers will keep on trying. The next big handheld FPS on the horizon is Killzone: Mercenary for Vita, and come "late August" all and sundry will be able to give the multiplayer a go when it enters open beta.
The closed beta kicked off today for the lucky, Sony explained in a PlayStation.Blog post, and the open beta will come late next month. As for exactly when, details are promised "really soon."
Killzone: Mercenary hits September 10. Look, here's dev Guerrilla Cambridge talking multiplayer: