Another issue regarding mobile phones comes not from interference but NETWORK issues.
Mobile phones use frequencies that are line of sight range. That means each mobile cell is about 25-35 miles in diameter (terrain and mast location dependant). Your mobile phone is interrogated by the network (similarly to transponder) about every 10 -15mins, so that the network knows where to direct any calls. If you are higher your phone can "see" more cells and responds to every interrogation, using up network capacity.
The point?
Well, I know a glider pilot who thought it would do no harm to fly with his phone on - it wouldn't affect any of the ac systems. Eventually his network sent him a really nasty letter telling him not to fly with his phone on. They can actually track phones by monitoring which cells the phone responds to - accurate to within 100m apparently.
Now I've distracted you with all this nonsense I'll let you get back to the subject.