If you take a look at the Modern Warfare 3 pre-order information, you'll see that both the PlayStation and Xbox versions of the game are marked as "cross-gen edition"  meaning that you'll not only be able to play them on last-gen consoles, but you'll also have access to the latest version at no additional cost if and ...

Call Of Duty Will Still Be On PlayStation\n\n A tweet from Xbox CEO Phil Spencer announced that this would not be the case with Call of Duty as Microsoft and PlayStation have signed a binding agreement to keep the shooter series on PlayStation following the acquisition of Activision Blizzard King.