Wow, that was quite fast! Apple, yesterday, released iPhone OS 3.1 Beta and SDK to developers for testing. This firmware will pack quite a hand full of new features that people have been asking for since the release of the iPhone OS 3.0 firmware.

Features found so far:

• Trimming video clips on the iPhone 3GS now offers the ability to save the edited version as a copy rather than simply overwriting the original file.
• Voice Control over Bluetooth is now available, allowing users to Initiate calls and control music playback via Bluetooth headsets.
• MMS is now enabled by default, but still not supported by AT&T.
• iPhone vibrates when rearranging Home screen icons.
• A “Fraud Protection” toggle is now available in Safari settings.
• iPhone startup and shutdown and app launching times have improved.
• New APIs allow developers of third-party application to access and edit videos.
• OpenGL and Quartz have seen improvements.

Just like other beta firmwares, this requires you to have a developer account with Apple.

- source: macrumors.com