Call of Duty: World at War hasn't hit the stores, yet, but nevertheless its successor has been announced already: in 2009 another part of the game is said to be released.
During a conference call Bobby Kotick, CEO of
Activision Blizzard, revealed, that the game will be developed. But the publisher will leapfrog studios. Therefore it is likely to be
Infinity Ward who will make the game, since they already did
Modern Warfare. The fifth part of the series,
World at War, has been developed by
Treyarch.
Furthermore, Infinity War is said to work on a Sci Fi project - transferring the
Call of Duty series to this genre could, according to
kotaku.com, be crazy enough to be successful but there is no evidence for this rumor.