Sony officially confirmed PlayStation All-Stars Battle Royale for the PlayStation Vita. The news and info about crossplay (PS3 users can play Vita users and vice versa) came at the PlayStation E3 press conference. It was displayed live, with two players battling on Vita while two others used a PS3.
All-Stars Battle Royale will feature cross-save support with up to three friends as well.
Lastly, it has a release date of Holiday 2012. For much more on characters and other information, you can check out the PlayStation All-Stars Battle Royal Wiki.