I've been witness to a phenomenon that's become quite commonplace these days- in-meeting multi-tasking. For a long time, theorists posited that people on their laptops and blackberries during work meetings were simply responding to being overloaded with technology and information (ignoring other more pragmatic explanations, like whether some meetings are boring, irrelevant or unnecessary).
A recent University Of Texas study just debunked that theory, finding instead that meeting multi-tasking behaviors are better predicted by organizational norms and acceptable behavior. In other words, if the leadership of your organization does it, so will the employees. If you don't announce clear-cut rules about it, your employees will do it. If you turn a blind eye or have a ban on it without any consequences, your employees will do it. So, what's the real way to stop in-meeting multi-tasking? Stop it. Difinitively. People only defy the boss as long as they know there won't be any reprocussions.