"Manufacturers have said there is a risk
It's always tempting to dismiss "pass it on" rumors as bunk, but the fact is that mobile phone manufacturers have warned consumers in the past against using the devices near gas pumps. This is an excerpt from a Motorola brochure for the Satellite Series 9500 Portable Telephone:
[T]his telephone has not been designed or approved for use in potentially explosive atmospheres. Areas with a potentially explosive atmosphere are often, not always, clearly marked.
Potentially explosive atmospheres include:
Fueling areas such as gasoline stations
Below deck on boats
Fuel or chemical transfer or storage facilities
Vehicles using liquefied petroleum gas such as propane
Areas where the air contains chemicals or particles such as grain dust or metal powders and
Any other area where you would normally be advised to turn off your engine.
Sparks in such area would cause an explosion or fire resulting in bodily injury or even death.
No laughing matter, apparently, nor should we suppose Motorola is trying to pull our legs. Similar cautions have been issued by other manufacturers, though industry spokesmen have more recently begun downplaying them, saying the actual risk is very slim, especially with newer and better-constructed models.
Still, in accordance with the maxim "'Tis better to be safe than sorry," signs forbidding the use of cell phones near gas pumps are becoming increasingly common in various parts of the world. Shell International explains its new policy in Asian countries thus: "Although driving whilst using a cellular phone is perfectly safe, we do not allow them to be used on the forecourt [of a service station] in case an electronic fault in the phone causes a spark." "
And, with all the recent stories of exploding phones which may be caused by "after-market" batteries, I'd rather play it safe.