The situation is a bit complicated. From having done a moderate amount of research over years, there are basically two answers: 1) Signs that you should not us

The situation is a bit complicated. From having done a moderate amount of research over years, there are basically two answers: 1) Signs that you should not use a cell phone at a gas pump are largely a result of a string of incidents in the '90s in which gas station fires occurred when the operator was using a cell phone. Causation was assumed and the warning decals were put on pumps. Later research by the Petroleum Energy Institute, an industry group, did not find any incidents that were actually caused by cell phones. The correlation may be due to a confounding factor, that people talking on cell phones are more likely to get in/out of their vehicle while pumping which could cause a static discharge. The PEI reports that, in general, improvements in vapor management in vehicles and fuel dispensers makes the risk of static discharge causing a fire low at modern gas stations. 2) General industrial best practice, and various safety regulations which are influential but not necessarily applicable to consumer gas stations, prohibit the use of electronic devices near flammable substances unless those devices are certified to be safe for that use. While many cell phones are probably "intrinsically safe" (do not involve potentials high enough to reasonably produce a spark), few are actually verified to that standard by the manufacturer (would need to be labelled "intrinsically safe" by the manufacturer following their safety analysis). In a safety-regulated environment they would thus be prohibited out of an excess of caution. On the balance it seems likely that cell phone use at the fuel dispenser is probably not a hazard, but it never hurts to minimize distractions and extra factors when handling something potentially explosive.