Apple on Thursday released a new version of its iPhone SDK for developers. iPhone SDK beta 2 includes Interface Builder, a component of Apple's development tools that lets developers create the interface for their applications.

That seems to be the only major change in the latest build, according to the SDK's read me, which continues to list some known issues. Apple says "this second beta is known to be incompatible with installation folders other than the default /Developer."

Given the importance of UI on the Mac, Interface Builder is a pretty critical tool in the development process, and some developers had chosen to hold off on their efforts until the SDK was revised.

Apple unveiled the iPhone SDK at a special event earlier this month, allowing developers to begin building applications for the iPhone and iPod touch. Several high-profile companies have already jumped onboard, demoing their applications at the event.

Highlighting the demos was AOL with a native AIM client; other applications from Electronic Arts, Salesforce and Apple were also shown.