According to UK game magazine PSM3, an announcement is coming in April. Activision may be planning to reveal Modern Warfare 3. There's no solid info on the game, but PSM3 speculated like this:
"Based on the ending of MW2, we'd be surprised if the story doesn't pick up with Soap and Price on the run, after they were set up by General Shepard."
There's no way of knowing right now whether this rumor is true or not, so take it however you want. We'll be further looking into this game (that doesn't officially exist) in the upcoming months.