Taking Calls on Your Mobile During Speeches

Should you or shouldn't you? It seems to be pretty obvious that under no circumstances should you take a call on your mobile during a speech. But even one-time Presidential hopefuls don't get it.

See this clip of Giuliani taking a call from his wife during a speech to the National Rifle Association. The audience reaction sounds positive, but I found this clip having read that members of the audience were appalled at Giuliani's action.