Unfortunately, Best Buy isn't using the promotion to grab new members—you need to have been a Reward Zone member since at least Feb. 21. But if you're a regular (free) Reward Zone member, it's $50 off the iPhone 3G this week with a new two-year activation. If you've got a Premier Silver membership (I don't know even wanna know what you have to do to earn that distinction), then it's a whole $100 off.
The lesson, kids, is that if sign up this week for Reward Zonemaybe you'll get $100 off the iPhone 4G when it comes out. [Best Buy - Thanks Brady]