While there is NO way I would want to be seated with hundreds of other passengers all chatting away on their mobiles
, I really do NOT believe there is any danger in using them, apart from the danger of maybe strangling a fellow passenger.
I have spent many many hours, although not on FBW Aircraft, where sometimes all 3 people in the Cockpit have been using mobile phones during cruise, and we never had any problems.
There was even a Company owned mobile phone FITTED to the Cockpit rear wall, just had the ringer disabled at low altitude so as not to be a distraction on take off or landing.