Daz,
This would put me off any airline. I fly a great deal on business, and the only respite I ever get, is when I'm on the plane. This is also true of E-mails. I know many travellers like myself, who find the one good chance they can get to clear their E-mail inbox is a long flight.
The idea of being in a plane surrounded by morons yelling on their mobile "I'm on the plane", would put me off flying with any airline.
So, get off your high horse about Ryanair, Daz, I would avoid any airline which offered this service, whether it be BA, Virgin or BMI.
But let us think about this carefully. The likes of BA, i have no doubt have already explored this, and are aware of the problems that could ensue on board, and realise it is not a good idea. Recently BA cancelled installation of the Boeing Connexion system for in-air internet access. I have no doubt this was based on customer feedback.
MOL is introducing this purely as a profit centre, not as a 'service'. I very much doubt we will see major airlines taking it on.
On a final point, I've seen you state many times that phone call revenue will produce cheaper fares. No it won't. It will keep MOL's pockets full. The same would also be true of your idea for coin slot lav's, just more profit for Ryanair. No passenger benefit whatsoever, despite what the Ryanair spin machine may be saying. Haven't you seen through the Ryanair spin yet?