iPhone OS 4 Beta is out and live in the wild. iPhone OS 4.0 beta is available for download for iPhone 3G, iPhone 3GS, iPod 3G and iPod 2G. iPhone OS 4.0 SDK is also available for download. Latest OS includes many new features including Multitasking, Fast app switching, Per-app SMS, App folders, A new Mail App, iBooks, Custom Backgrounds, Game center and many more.
Availability : The beta version of iPhone OS 4 software and the SDK are available immediately registered developers at the iPhone Developer Program is available for developer.apple.com. iPhone OS 4 for iPhone and iPod touch customers this summer will be available as a software update. A version of iPhone OS 4 for the iPad will appear this fall
In order to download and install you must be a developer, if you are needless to say go ahead and to Apple Developer Site [Click Here] to download iPhone OS 4.0 beta.