The new beta of the upcoming 4.0 reference release includes "significant API additions" as well as a new tool that makes it easy to provision a device for development, developers familiar with the new software report.
The new APIs largely flesh out the new multitasking and background processing features related to audio, VoIP telephony, location services, and Task Completion. Apps can now request a ten minute period to complete a task, up from an initial five minutes.
The new build also includes a new animation effect in the multitasking user interface, which swipes the current app out of view to reveal the app the user chooses (below, from the Italian iPhoneHacks.it).
Improvements to GameKit (publicly branded as Game Center) and expanded support for Internet mail features are also rolled into the new release, as well as support for LLVM-GCC and Clang LLVM as new compiler options for iPhone development.