Can I use my 3G case with the 3G S?
Yes! While there are a few manufacturers that are now advertising cases for the 3G S, there are no physical differences from the 3G. So any existing cases or accessories you may have should work with the 3G S just fine.
Well then, what exactly is different about the 3G S?
Although the physical appearance didn't change, there are a few significant changes to the hardware in the 3G S. Most notably, the CPU, video chipset, and memory have all been upgraded, as well as the addition of a digital compass, faster 3G radio, and improved camera lens. There are also some software enhancements to allow voice control, video editing, and more.
Can't I just install 3.0 and get the same features?
Not quite. Installing the 3.0 update will get you several of the new features, such as copy and paste, voice notes, MMS, and tethering (if your carrier supports it, anyways), but some of the features will only be available on the 3G S. Things like voice control, video editing and sharing, compass navigation and accessibility improvements take advantage of the new hardware found in the 3G S to provide a better user experience, so Apple doesn't offer those features to users of older iPhones.
Can I upgrade from my iPhone or iPhone 3G?
Yes! From the hardware side of things, upgrading is as easy as plugging in your new iPhone to iTunes, then selecting that you want to restore your backup to the new phone. Alternatively, you can set it up as a new phone, and just sync the apps, music and other items that you want without restoring the full backup.
From the cell phone carrier side of things, upgrading is a bit more complicated, depending on when you purchased your phone, and the terms of your individual contract. Luckily, some providers are offering special terms to encourage customers to upgrade.
Where can I find out more about the iPhone 3G S?
If you're starving for details, our friends over at Engadget have a full review of the new iPhone, including an unboxing gallery and sample videos. If you're looking for a side-by-side comparison to the 3G, Walt Mossberg chimes in with his take on the All Things DIgital blog. And, as always, you can check out our iPhone 3G S articles here on TUAW.