There is no evidence to suggest mobile phones are a risk at fuel stations other than some plonker chatting without watching what he/she is doing and spilling fuel over the forecourt. In reality very few vehicle fires are caused by fuel - most are caused by electrical wiring fires but once they get a hold everything can be consumed.
I agree that the mobile phone thing is incorrect. Someone put two and two together and made five. The actual problem was American fuel pumps, which can be latched into the on position once inserted. Drivers were putting the nozzle in, then repeatedly getting in and out of the car. The static was discharging a spark around the fuel filler just as the vapour was being displaced by the fuel being pumped in.
Often, the problem was made much worse by the driver's reaction, which would be to step back while still holding the nozzle (still latched on) and now pouring petrol all over their burning car.
I asked a fireman once what was the biggest cause of vehicle fires in an accident and he replied either a short in the wiring system or brake fluid spilling onto a hot exhaust. The amount of electrical energy required to ignite a fuel/air mix is actually quite high - if you have ever had a shock from an HT spark plug lead you'll know roughly how much
To get reliable ignition, you need lots of energy. For the possibility, you only need a spark. IIRC, you can get a spark through shorting out a 1.5v AA battery. The same may even be true of a button cell.
Maybe I'm just bitter because I had this idea too a few years back, and dismissed it because I thought I'd never get away with putting an electrical device near the fuel filler. I could have been rich by now. Ho-hum.