MacRumors.com

Apple changed their home page today with a photo of an iPhone and MacBook Air with the title "Calling all developers", reminding visitors that early registration for the World Wide Developer's Conference ends on April 25th, 2008.

Meanwhile, Apple also quietly released the 4th beta of the iPhone SDK. Beta 4 adds at least one much requested feature: OpenGL ES support within the iPhone simulator. Previously, developers had to install directly to their iPhone to run OpenGL applications.

"The fourth beta version of the iPhone SDK includes Xcode IDE, iPhone simulator with Open GL ES support, Interface Builder, Instruments, frameworks and samples, compilers, and Shark analysis tool."

Developers are continuing to work on iPhone/Touch apps and games to ready for the June launch of the iTunes App Store.