I have yet to read a scientifically produced, peer-reviewed article on the subject proving or disproving anything. The only info seems to be hearsay, but is saying that the potential dangers far outweigh the rewards.
From personal experience the only effect seems to be the annoying noise in the headset, and as Bullethead said, the battery going flat faster (which apparently is due to the phone boosting it's signal as it hunts for reception)
But really, who needs to use the phone that urgently anyway? The cabin of an aircraft is one of the very few phone free places left
