Smart phones emit radio signals. They are extremely powerful and interfere with almost everything in their path. This can easily cause disturbances such as someones radio listening in to your conversation, finding out you are a secret Al Quaeda terrorist. They in turn tell the police, who come to your house and mercilessly beat you. OR It could interfere with nearby appliances, such as the toaster, causing your neighbours toaster to explode into a million peices, killing him, burning the toast, and setting fire to the house. Then the house next to his catches on fire, and in turn the whole city is burned to the ground. Including the Nuclear reactor plant, which, on explosion covers the whole area in toxic waste, making everyone become flesh - eating zombies, congratulations on your new phone, dumbass.