One day has passed since Apple gave developers a sneak preview of iPhone OS 4.0, and already there's new (NDA-breaking) information floating around about the other 90-some features that Steve Jobs didn't discuss at Apple's media event.

In addition to renewed evidence that Apple may add a front-facing camera and other camera-related features, developers with access to the beta have told Ars about even more tidbits buried within, essentially making OS 4.0 a piñata of API goodies for devs to beat on.

Thursday's announcement immediately turned up evidence that Apple might be adding a flash to the iPhone's camera, thanks to functions named VCaptureDevice.hasFlash, AVCaptureDevice.flashMode, and AVCaptureDevice.hasTorch. Apple is allegedly investigating LED flash options, which would make such a feature very BlackBerry-like. Additionally, the latest iPhone SDK continues to contain hints about a front-facing camera as well as iChat support.

That's just the tip of the iceberg when it comes to the hidden gems in OS 4.0. Several developers told Ars that this is the single biggest update to iPhone OS that they have seen. The SDK contains plenty of references to expanded A/V capabilities and media handling. There is also expanded support for VoiceChat—particularly within Apple's just-introduced social gaming platform GameKit—as well as a perplexing reference to Microsoft's Direct3D.

There are also a number of API references to the creating, reading, and editing of media, leading some developers to believe that Apple could build something like iMovie or GarageBand for iPad (though third-party GarageBand-type apps are already quite common). In addition to video-related references like layering and frame durations, developers can also get metadata from all manner of video and audio files.

This is in addition to details about some of the features that were announced yesterday, such as access to accelerated math libraries (such as linear algebra, vector digital signal processing, and more), the ability for apps to mark files as "protected" (part of Apple's new enterprise features), and direct access to QuickLook, tap to focus, and the camera's white balance.

The final version of iPhone OS 4 isn't expected to appear until sometime this summer, likely coinciding with another iPhone hardware refresh from Apple. As the rest of us wait for the chance to play with the new software, there's sure to be more leaks about what we can expect to see in a few months. Are there any unannounced features that you're keeping your fingers crossed for?