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I would find it pretty hard to believe that the RF emissions alone could induce enough current in anything to cause an explosion. MAYBE if you had one of the old 3-watt construction-site "bag phones" you could generate enough flux. However:

1) There are reported cases of cellphones catching fire, due to problems with the battery;and

2) Cellphone batteries occasionally dislodge, causing sparks.

Now, I'd admit that you would have to do this in a very fume-rich atmosphere to cause a fire, which isn't likely. And the reason for the regs is RF, not battery-related. Kind of like the rules that say you can't run a walkie-talkie on a construction site when blasting is in progress. . .

However, Michael brings up another valid point, which is INATTENTION. You are NOT supposed to get back in your car with the nozzle plugged in. You are NOT supposed to wander around the gas station while your car is fueling. Those of us with 911's rarely do, anyway, due to the need to hold the nozzle upside down to get the gas in (the old s-shaped fuel pipe), or the need to keep bystanders and the attendant from doing STUPID things like leaving the gas cap on the paint or on the windshield.

Finally, there are REAL reasons why use of cellphones and other RF transmitters is prohibited on board aircraft. The first is the old "line-of-sight" transmission problem which was discussed here before-- the number of cell phone frequencies is fixed, and if you go to high elevation, you are capable of communicating with a large number of towers at the same time, which screws up the system. Yes, even with your little .8 watt Nokia.

The other reason is that every little .8 watt Nokia uses a circuit called a "local oscillator" to lock on to the receiving frequency. This is basically a circuit that generates the baseline frequency in the phone, and then compares the received frequency to the baseline-- the difference is the signal. The phone itself generates RF, and you don't want it in proximity to, for example, the DME antenna on an airliner, which operates in the UHF spectrum. There are also dozens of reported cases of VHF nav radios experiencing interference. Most airplanes don't use LF/MF nav much (ADF) but they are VERY susceptible to RF interference. I don't have an ADF in my plane, nor do I actually know anyone who does, but the next time I'm around one, I'll wave my cellphone next to the antenna and I bet I can get the needle to move.

Is the RF enough to induce noise, making the DME unreadable, causing you to fly past the missed approach point and into terrain? Is it enough to cause a full-scale localizer deflection at the Inner Marker? Doubt it.

But the slight risk, multiplied by the significant magnitude of harm, outweighs the need of some fat-assed jerk to have their cellphone out and operating during the final approach segment. And ditto for the well-meaning but clueless person at the Gas Station. Shut it OFF and give us all a break.

And shut the damn thing off in the movie theatre while you're at it.