More specifically, developers testing the release overnight report that iPhone Software 3.1 will allow you to "Save a Copy" of video recordings that have been trimmed, rather than being forced over-write the original copy of the video, as is the case in iPhone Software 3.0. The update will also allow you to save to your photo album videos that have been sent as email attachments.
Another noteworthy enhancement is the ability to issue commands to the iPhone's new Voice Control feature over Bluetooth headsets. Spoken commands when running iPhone Software 3.0 aren't picked up by Bluetooth headsets, and are instead channeled through an iPhone's built-in microphone even when a headset is connected.
Several developers are also reporting that the MMS button has resurfaced in the Messages application, possibly signaling plans by AT&T to begin supporting picture, sound, and video messages around the release of iPhone Software 3.1. Although developers testing yesterday's beta report being able to insert multimedia into messages, those files are still rejected by the U.S. carrier's network.
iPhone Software 3.1 also reportedly improves battery life on the iPhone 3G S, updates the "Carrier" profile for U.S. users to "AT&T 4.2," as opposed to "AT&T 4.0," and provides vibration feedback when home screen icons jiggle to symbolize they're ready to be moved or rearranged.
Other changes include modified iTunes Store icons that rearrange themselves back to default after opening and closing the app, and the previously-reported developer hooks that provide access an iPhone's video recording and editing functions, as well as a handful of new extensions for the OpenGL ES graphics library that developers can use to improve graphics performance in their apps.