Apart from having to listen to someone discussing their irritable bowel syndrome aside, mobile phone use (and implications on safety) in flight is one of those rules that is a "we don't know so....."
Thing is it is not cut and dried. Having flown a lot in Asia especially the subcon, IF mobiles impacted flight systems, then aircraft would be falling out of the sky like flies. Fact is they are not. The number of phones chirping and cheeping as you descend into (say) Mumbai is pretty amazing.
The FAA is unsure too...
Are Cell Phones Dangerous In Flight? (VIDEO)
And with people like EK allowing in flight usage....
So next time, before you get all panicky while sitting on a DASH and some teen is sexting his/her friend, just plug your ipod in and listen to some soothing music.