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According to the movie Snowden placing a mobile phone in a microwave oven disables it. I don't know if that would work for sure but it sounds plausible to me.
If you want to disable the phone permanently just turn the oven on for a while.
Info from the local police and media: A few years ago a bunch of guys decided to terrorise a local business owner (illicit drug related). They were all "Bikers" or "associates" including the business owner. They met at a house near the place of business and they all turned off their phones and left them at the house. They then travelled to the place of business and proceed to beat up the owner and damage the property (car crash repairs). But things got our of hand and the business owner was killed.
They all left and went back to the house to collect their phones... Can you guess what they did when they got back to the house?
The police could see from the phone records that all of the phones were turned off and then back on again at the same time and location. The house was a "safe house" but the police had known about it for a long time. The smart thing to do would be to leave their phones at home but apparently being a "Biker" or "associate" doesn't require a lot of intelligence.
These idiots used a "custom made secure mobile phone" for world wide communication via txt. As it turned out it was a device that your FBI with the assistance of The Australian Federal Police built using a generic smart phone sourced from China. This was "made available" to the criminals through and informant and used globally! Yea well, not the sharpest knives in the draw... lol
http://forums.pelicanparts.com/off-topic-discussions/1095338-anom-world-wide-sting.html