Infinity Ward community chief Robert Bowling has let slip that a Call of Duty 4: Modern Warfare sequel is in development. Speaking on his blog, Bowling Twittered that voice-overs for "Modern Warfare 2" have already been recorded. "Reviewing some radio-chatter VO we just finished recording for Modern Warfare 2 today. 'Cujo Two-One this is Vulture, solid copy on all,'" said Bowling. That's the first we've heard of a Modern Warfare sequel, despite Activision quite openly planning more instalments in the Call of Duty franchise. This fits with the alternating Call of Duty development cycle between Infinity Ward and Treyarch, too - the latter having delivered Call of Duty: World at War last year. We've asked Activision for clarification, but we don't expect to hear more for a while. There's no other information at the moment, but we'd be surprised to see a Christmas period without a Call of Duty game.