Beta 3 is only accessible to those with an existing developer account. Labeled build 7C116A, it weighs in at 307MB.
Apple also released a new iPhone SDK for OS 3.1. The SDK build is 9M2808.
Those running Beta 2 must update by midnight tonight (local time based on each individual device) in order to continue using the device without interruption.
As revealed with the first beta release, 3.1 adds Bluetooth and video features. Users can now invoke Voice Control using a Bluetooth headset rather than a wired headset or the built-in microphone. When editing video clips, users can save a copy of the trimmed video instead of permanently losing the discarded ends.
Since the second beta, iPhone OS 3.1 has allowed developers to connect to and work with a system wirelessly, without the tether of a USB cable.
At least one developer has been told that the new update will allow for augmented reality apps, which overlay information and controls on top of real-world objects seen through a camera.
Unofficially, iPhone OS 3.1 is anticipated to be ready by early September, just in time for Apple's by now yearly iPod updates — and the seemingly probable release of an iPod touch with a camera that could take advantage of augmented reality when using Wi-Fi.