I heard that the british anti-terrorist team S.A.S. use this kind of technoledgy non stop. So when somone trys to use their mobile a beeping sound comes instead of the ringtone. So then the caller thinks it's busy. Same happens if somone try's to call them. But then again I guess they have the permision for that kind of thing. After all. They are the best of the best. Well. That's what I've been told.