It is said that using a cell phone whilst filling a car could start a fire or explosion. I always thought that the idea was silly given that the RF produced by the phone is really strong. The reasoning is actually for a totally different reason. The problem is not the cell phone per se but rather the battery connections within the phone, and any other portable device for that matter. The thinking is that when the batteries are of poor quality or neglected that they may arc across their contacts to the portable device causing the fumes to ignite. Yes of course you will say that you cell phone is a nice sealed unit but that wasn't always the case, some cell phones had nasty battery terminal and of course little Johnny might use his phone with and inappropriate battery strapped on the back.
Food for thought. The interesting fact that caught my attention was that we tend to think that the problem has to be the RF signal because the device is a transmitter rather than thinking laterally and looking for other potential issues.