Yes Davethelimey, it very dangerous: Switch on your mobile phone on Taxy and within seconds a crew member will whack you round the back of the head with a safety card. Can be lethal, papercuts.
Seriously though, I'm no avionics expert but rumour tells me it can effect fire extinguishers on engines, and instrument panels on the Airbus. If anyone would care to quote the actual facts here I would be very grateful.
