Apple released the third beta version of iPhone OS 4, only to temporarily rescind it due to an apparent problem with the installation process for the accompanying software development kit.

The beta OS versions are available only to registered developers via the official iPhone Dev Center. The 9to5Mac website picked up on the developments and other news sites and blogs are digging up details. One of the key new elements in the 4.0 release is limited multi-tasking, being able to run several apps or functions at once. Apple last month previewed OS 4.0 and surprised some with the software's business features. 

9to5Mac writer Mark Gurman spotted one new element in the beta 3 release: a new widget-like interface for the phone's iPod functionality. The controls are revealed as buttons when you flick to the left the first pane of open apps: a fast-launch button; some music controls; and an "orientation lock" to keep the app's user interface in portrait mode. One tap locks or unlocks. In the existing OS version, users double-click the phone's home button to bring up a somewhat similar set of controls.

Wired's Charlie Sorrel goes into a more detailed analysis. He notes the iPad offers a screenlock in the form of a dedicated hardware button. The iPhone lock on-screen button is exposed in the new multi-tasking dock that appears when you tap twice on the home button. This dock lets users switch between open applications.

"The iPod buttons have also moved to this control strip, and we presume that they replace the dialog panel which pops up when you double-tap the home button in the current iPhone OS," Sorrel writes. "You also get a button to access the iPod app."

Sorrel also noted that each app in the multi-tasking strip has a "quit" button associated with it. "This looks a lot like a task manager," he writes. "I'd be constantly worrying that there were too many applications open, sucking my battery. "These new buttons are accessed in the same way as the search screen on the current iPhone: Once you have accessed the dock, you swipe to the right to reveal this new panel. At least this part makes sense, although the once-simple iPhone OS looks to be getting a lot more complicated."

The next version of the iPhone smartphone is expected by many to be revealed at Apple's Worldwide Developers Conference in June in San Francisco.