According to Mark Rein from Epic Games, the PC and PS3 versions of Unreal Tournament 3 have the possibility of being enabled for cross platform play.
To what extent this will be included, still remains a mystery.
Now UT3 makes for a complete experience, including mouse and keyboard support thanks to the beautifully crafted FragFx. PSU can't wait to see the mayhem of PS3 players and PC players duking it out this coming November, however it is implemented.
Source: Epic Forums