An anonymous reader writes "When President George Bush visits Sydney, Australia for the APEC Summit in September, all cell phone calls within the radius of a football field will be suppressed. The president's motorcade will be shadowed by a helicopter equipped with signal-jamming equipment. Terrorists have used mobile phones to detonate remote-controlled bombs in Iraq and elsewhere in the world."
There are other ways to detonate explosives remotely. Doesn't seem like the smartest thing to let potential enemies know of such plans in advance.