I don't think anyone has said it's OK for BA but not for Ryanair. I'm not totally sure what it's in reference to either.
What BA are doing when they roll out OnAir on the A318s this autumn is setting the system up to allow SMS and data (email) only - not voice. Then, if there is demand, they will activate the system for voice too.
I think this is a better way of dealing with it. You won't then hear "yeah I'm on the plane" every two seconds. And I doubt anyone will be ringing anyone on the overnight flight back to the UK.
I do think though that if a silent (in terms of mobiles) cabin is to be employed, then perhaps a clause "you must switch your device to silent/vibrate" should be included.
Me thinks Ryanair could become an unbearable airline to travel on... Well, aside from the no luggage, no carry on, no wheelchair or pushchair, no check-in desk, no contact with a human on the ground, everything must be done on the internet or else policy that's coming into full effect...