Originally Posted by Gordy
As far as I know, in the US it is enforced by the FCC. If your phone is transmitting from an airborne aircraft, the slant range of the signal is greater and is received by many receiver sites. Because the signal hits lots of receiver sites, they are unable to track it and it also reduces the amount of users that can use the system. Of course I may be wrong.
I worked flying for a cell phone company for a little while, we worked with the engineers locating places where the transmissions of several cloned phones had just been programed so that the police could show up and politely ask them to stop.
They told me about this system saturation due to the cell phone reaching so many stations at the same time. But so many people used phones on helicopters in Mexico City that the companies resorted to pointing the antennas downwards, now its almost impossible to talk from any tall building, much less a helicopter.