I can't remember the source but I did read that the significant danger with mobile phones is dropping them while refueling and the battery pack separating/breaking. If it is on there is a risk of a spark. This was a while ago when battery packs were often easily removable but the main point was a spark occuring near the ground where the dense flammable vapours would pool.
best not to drop your flashlight or I-pod as well
Best to opt for the full service option and let the attendant off himself instead