Then there are the alleged mobile 'phone calls from the planes whilst at altitude. In 2001 few calls could reach ground stations, especially if many people on a plane were calling at the same time. A curious number of the calls not only reached the recipient but were recorded.

Researchers have pointed to vice morphing equipment as used by the CIA and suggested that the calls were hoaxes. One 'caller' made a big mistake by asking to speak to a close relative using both the person's first and last name.

Voice changer - Wikipedia, the free encyclopedia