If you’re the owner of an iPod Touch, iPhone 3G, or iPhone 3GS, you’ll want to get your device plugged into a copy of iTunes today because the upgrade you’ve been waiting for is here.

New features of the free operating system update include support for iBooks, more digital zoom for your camera, the ability to sort your applications and shortcuts into folders, creating playlists on the go, and multitasking.

While these features might seem like a perfect upgrade to an already perfect phone, be warned that depending on what model you’ve got, you may not get everything on list.

Apple’s iOS 4 might have “over 100 new features,” but reports are already coming in that the iPhone 3G is missing some of the cool things.

The big thing that’s missing in action for iPhone 3G users is multitasking, something that Apple had previous mentioned wouldn’t be available for non-3GS users. We haven’t gone through and tested everything yet, but early reports suggest that home screen wallpaper support is missing as well as the iPhone supporting Bluetooth keyboards.