Why you're not allowed to use your phone near gas stations

I've got to tell you, that I didn't believe in this myth. The energy from the mobile phone is so little that, you aren't able to get a spark. Things change if the energy is "stored" in the crumpled aluminum foil, and making lots of calls. The only realistic scenario I can come up with is that your car or some other piece of metal is already statically charged and your phone is the water drop that fills the glass. Anyway, it's very unlikely!