Honestly, there's not much you can do to fight the lines tomorrow at Apple and AT&T stores. But at least you can use the Line Snob app to get a sense of how long a wait you're in for.
Line Snob depends on people who are already in lines (and the venues themselves, in some cases) to send back data for those weighing the wait back home. It's normally good to check bars and airports and events and such, but will come in particularly handy tomorrow as you mount an iPhone 4 plan of attack. Line Snob is a free download—just make sure that your city is one of the 25 covered. [Line Snob]