.22 Caliber 4 Shot Cell Phone Gun
If you get asked to test your cell phone at the airport, this is the reason. Because cell phone guns have been discovered.
The attached video clip shows how cell phone guns operate. Beneath the digital phone face is a .22 caliber handgun capable of firing four rounds in rapid succession using the standard telephone keypad.
Go HERE to see the video of it in action.
You can find a lot more information here, including that this is not a hoax, at Snopes.