While this would be good for users who lose (or are robbed) their phone to keep a thief from using it, wouldn't this be an easy way for someone with malicious intentions to destroy the cell phone of any user they wanted. Surely someone would figure a way to do this. Sounds like this could result in more damage than good.
With this, nobody would be allowed past airport security...
Terrorist: I'd like to check in my bags...
Airline Personal: Are you carrying on that box?
Terrorist: Yes...
Airline Personal: All set, please go to the airplane!
Then, On the plane...
Terrorist: There's enough people... I should open the box...
Passenger1: Uh-oh... My phone is beeping!
Passenger2: Ahhhh! My Gameboy Advance!
Airplane Pilot: My Palm Pilot With Navigational Assistant!
Terrorist: Whoops... Guess My Box Had One Too...
After a Fiery Explosion...
News Reporter: ...after what appears to have been a terrorist explosion. Airline personal have said that no high-explosive bombs have been brought aboard, but there was an unknown beeping shortly before the explosion...