Probably a hoax:
http://urbanlegends.about.com/library/bl-c...e-gas-fires.htm
http://www.trendmicro.com/vinfo/hoaxes/hoa...e+Ignition+Hoax
http://www.wisinfo.com/thereporter/news/ar..._12312233.shtml
"An e-mail hoax forwarded through cyberspace for the past two years is loose in the Fond du Lac area, causing some alarm about cell phone usage.
The e-mail, which has no traceable origin, discusses the dangers of cell phone usage at gas stations — specifically, how the ringing or answering of a cell phone can be the spark needed to ignite gasoline vapors and fumes and start a gasoline fire.
The e-mail details three such incidents that supposedly occurred at Shell gasoline stations. Contacted at Shell’s corporate offices in an effort to verify the validity of the e-mailed contents, Shell officials dismissed the e-mail as an Internet hoax."