X-Quork,
An integrated aircraft phone system will use its own dedicated external antenna - usually via sattelite.
This is a big difference from internally radiating cellphones. These can (and have done) affect the most differing sysytems from comm & nav - radio based systems, to electrically/electronically controlled systems on board - from compass to hydraulic and air conditioning systems.
Any system having a cable within oscillation range of any other passenger held electronic device may be susceptible. It depends on the screening of the hand held device and of the aircraft cabling.
Suggest NASA and the CAA as a source of data.