Will this product work with the iPhone 3G?

Yes, the PowerDock was recently approved by Apple for use with iPhone 3G.

Initial units of the PowerDock do not have a 3G universal dock adapter included. To get one, click "Buy Now" on the PowerDock page, where they are available for $1.99. At retail stores, PowerDock units packaged with the iPhone 3G listed as compatible will have the 3G adapter included.