AT&T is set to release an AT&T Upgrader app for the iPhone 4S. The app is supposed to simplify the upgrade process by letting iPhone owners know what type of upgrade they're eligible for, how much the iPhone 4S will cost and then let them place their pre-order, all through the app.
If you don't have an AT&T iPhone, you can still pre-order without heading to an AT&T store by heading to http://www.att.com/phoneupgrade (though the site is currently locked for internal testing). The AT&T Upgrader app isn't live in the App Store yet but we'll be sure to link it once it's a go. Sorta poetic to use your old iPhone to get the new iPhone. [AT&T]