Don't forget about the used market. There's a slew of people selling their iPhone 4 to upgrade to the 4S, and people are still buying the 3GS. If you really need to upgrade, but don't care if you're getting the latest and greatest, it looks like you can sell your 3GS for $200 and buy a 4 for $400 right now. If you're going to use it on Tmo's pre-paid, just make sure the new phone has an unlockable baseband.