Q: Can I sync my new iPhone 3G S with the same iTunes library as my iPod classic?
A: Most definitely. The iPhone 3G S will simply sync to your iTunes library like any other iPod device would, and you can easily sync multiple iPods and iPhones with the same iTunes library.
When you first connect your iPhone to your computer, iTunes will take you through a quick setup wizard to ask you how you want to sync content with it. After that, it will simply show up in your iTunes Devices section in the same way that your iPod classic does. You can even have both your iPod classic and iPhone connected at the same time. In fact, there’s no practical limit to the number of iPod, iPhone and Apple TV devices that you can simultaneously.
iTunes maintains separate sync settings for each device, so you could for instance choose to sync all of your content with your iPod classic while only syncing selected playlists with your iPhone 3G S, or you could choose to manage the content on one device manually and use automatic sync for the other.