I don't know whether I'd have the guts (or the rudeness) to carry through on this, but if I found myself on a long flight forced to listen to endless cell phone conversations from all around me, I'd be greatly tempted to pull out a "boom-box" tape player and switch it on with some possibly unpleasant music or audio at similar volume in retaliation.
Flying, which used to be a moderately pleasant occasion to relax, read, work, or just sleep, has become a more than sufficiently unpleasant experience in recent years. If cell phone users are going to pollute the audio environment in the cabin sufficiently to make it even more unpleasant for others, surely so can we music lovers ...