Telephones take flight

That icon of technology, the passenger jet, was one of the last places in the developed world in which it was impossible to make a telephone call. Now this bastion of isolation is succumbing to digital technology. In-flight passenger telephone services, known generically as airborne public correspondence (APC), have now become an established fact of air travel. Here, the author describes how there are two quite different approaches to providing these services for the passenger: some systems use satellites to provide the radio bearer between the aircraft and the ground, while the so-called `terrestrial´ systems use direct air-to-ground radio links