CafeClub:
How many 777 flights had there been before YMMM?
t1grm
There are some British Standards for the RF intensity level allowed before ignition occurs, based on some Sheffield university work. There's also a DEF STAN on allowable RF levels around munitions and fuel - I can't remember which one, and I'm not at home to look it up. But it's lot higher than you get from a mobile 'phone. The limitations you see on garage forecourts around petrol pumps came from the discovery by illegal CBers running around 50 or 100 watts led to the petrol pump under registering, rather than ignition problems.
It's thought by many that an arc can cause ignition, but in fact, the arc has to have a certain amount of energy, depending on air/vapour mix. Unless there is enough energy, it won't catch.
More of a problem, is that the person using the 'phone gets distracted and does something silly (like texting while driving!), or if the thing is dropped and the battery sets fire to some of the bits, maybe because of a short circuit.