We don't have an iPhone app, but we have a site optimized for the iPhone available at m.fuelly.com. So you can browse to m.fuelly.com with Safari on your iPhone, use the "Add to Home Screen" feature, and you'll have it mixed in with your other apps.
an iPhone app (either just for jailbroken guys, or an AppStore official one) would be awesome. It would permit us to save the data and have it upload later, incase we did not have reception at the fill-up station.