I need to know how the application data is stored? Take, for instance, a Checkbook application. We have 2 iPhones, about to be 3 iPhones, that share one iTunes account. I have the Checkbook app on my 3G and I will be taking my son's new 3GS from him once he upgrades and giving him my 3G. (Mean Dad I realize). Obviously, I don't want to lose my Checkbook data. So is it stored by the phone Serial Number, or the phone name, or by some other means? Thanks in advance..