iphnappsApple has released the 2nd iteration of the iPhone SDK (software development kit) beta on its website. This version is believed to offer only one significant upgrade, but it’s a big one: the Interface Builder that was promised at the SDK event earlier this month (our coverage).

This crucial part of the SDK will let developers easily create applications that have the look and feel of the ones Apple develops natively. Items such as Apple-styled buttons can now be added by simply dragging-and-dropping.

Some iPhone developers were waiting to get started on their applications until this tool arrived, as InfoWorld notes. Many users in popular Apple forums were also confused as to why this tool wasn’t included in the first beta.

Excitement continues to build around the iPhone SDK as we draw closer to the iPhone 2.0 software launch in June, which will allow users to use third-party applications. Even Microsoft wants in on the action (our coverage).