I noticed that the appearance of the no cell phone signs came around
the
same time that gas stations started running audio commercials through
speakers at the pump.

Interesting observation.

we dont have audio commercials at the pump here in New Zealand
(thankfully),
but we do have the no-cellphone signs though. It is likely to be no more
than corporate paranoia - can we get our asses sued off if we dont tell
people to do this.......I suggest we blame the lawyers


Cellphones can only ignite gasoline fumes in the vicinity of
cars prone to unintended acceleration.

David