Apple has posted the iPhone SDK 3.1 beta and iPhone OS 3.1 beta on the iPhone Dev Center. Apple says they’re for developers and testing only and should be installed on devices dedicated to iPhone OS 3.2 beta software development.
The iPhone SDK provides developers with the same set of application programming interfaces (APIs) and tools that Apple uses to create its native applications for iPhone. iPhone DSK 2.2.1 is available as a free download for Apple Developer Connection (http://developer.apple.com/) members.