Apple has released iOS 4.0 for the iPhone, iPod touch via iTunes and is available as an update. iOS 4 works with iPhone 4, iPhone 3GS, and iPhone 3G, iPod Touch 2G, 3G. This contains over 100 new features, including much awaited features like Multitasking, ability to quickly move between apps, Support for audio apps to play in the background, Photo and camera improvements, folders, even better Mail, iBooks, and more. Below are links to download the iOS directly from apple site.
To install these via iTunes, hit the update button, while holding down the Shift button which lets you any firmware from the hard drive.
Note: Recommend all jailbreakers and unlockers hold off a bit before installing new firmware until we post how to.