Apple has released the iPhone SDK 3.1 beta to developers. i Phone SDK 3.0.1 tends to do for minor updates and bug fixes.

email text from Apple to developers

iPhone SDK 3.1 beta and iPhone OS 3.1 beta are now posted to the iPhone Dev Center. These versions are for development and testing only and should be installed on devices dedicated to iPhone OS 3.1 beta software development. Please read the iPhone OS Pre-Install Advisory and the iPhone SDK 3.1 beta release notes before downloading and installing.

[ Techcrunch ]