The new version of the operating system (a.k.a. firmware) is now available for iPhones and iPod Touches. This is the software that will be running on the soon-to-be-released iPhone 4GS.
The download is free for both iPhone and iPod Touch users, but it is incompatible with first-generation models of either device. The iPhone 3G will support most iOS 4 features except multitasking and home screen backgrounds.
I’ve had it running on my iPhone for a couple of days and I’ll say that it is well worth the effort to update, although it hardly seems like a major o/s iteration.
If you want to update your iPhone/ iPod Touch, you’ll first need to make sure you have iTunes updated to version 9.2. From there, simply connect your device and iTunes should prompt you to install the update.
There are dozens of great reviews out there that comb through the new features in detail, but here is a great “getting started” guide: