Today, Apple releases the iPhone OS 3.1 beta 2 to developers for early testing:

iPhone SDK 3.1 beta 2 and iPhone OS 3.1 beta 2 are now available on the iPhone Dev Center. These versions are for development and testing only and should be installed on devices dedicated to iPhone OS 3.1 beta software development. Please read the iPhone OS beta Pre-Install Advisory and the iPhone SDK 3.1 beta 2 release notes before downloading and installing.

What's New

According to developers who have played around with this beta OS,

1. (For iPhone 3GS only) Now Video Editing gives you the option to trim your clip then “Save as copy…” rather then replacing the original video clip.
2. (For iPhone 3GS only) Voice Control now works over Bluetooth.
3. iPhone now vibrates when arranging icons.
4. Updated AT&T profile to 4.2 and probably enable the support of MMS
5. The baseband version is updated to 5.08.01. This will fix the holes used by ultrasn0w and makes ultrasn0w fail to unlock iPhone 3G. So, don’t upgrade to iPhone 3.1 beta if you need to unlock iPhone 3G
6. Minor tweak for Calendar app. The event alert will also show the location in the popup alert.
7. Enable copy & paste in iPhone dialer keypad.

As usual, Apple does not disclose the release date of iPhone OS 3.1. But I expect it’ll release very soon. And, for those who are using ultrasn0w to unlock the iPhone 3G / 3GS, please stay away from iPhone 3.1 beta (at least for now). Otherwise, your iPhone will be locked again.