Apple has released an updated version of the iPhone software development kit, adding support for a popular tool.
The new SDK is available for downloading on Apple's site, and now comes with Interface Builder. That tool allows you to design user interfaces in line with Apple's human interface guidelines, which is a requirement for iPhone applications.
This is a helpful reminder that the SDK is a beta product until June, when it's scheduled for a formal release. After an initial bottleneck, Apple has started accepting developers into its program to begin developing and testing their applications for a June release.