In a frank IRC chat yesterday, Epic boss Mark Rein states that there won’t be PC-PS3 cross platform play, at least at launch.
“The biggest challenge in doing cross platform play is syncronizing the builds such that the build on the PC is 100% compatible with the build on the PS3” he says. “This doesn’t completely rule out adding this feature at some point in the future after the game has settled down and we’ve been through a few.”