A: Plane flight control systems wouldnt be connected in software to a radio of any kind. Unless you change the firmware of virtually every computer in the plane. Which is impossible. The plane might not even have the hardware to do it.
B: Plane radios do not operate at 900 MHz like GSM.
C: The interface isn't fast enough to get past encrypion, even if the functionality does exist.
Whoever believes this crap is smoking crack