Animated Page Twist Transition (not the book flip)... how did they do this?

I’ve seen this on several sites and while I imagine its done using several imported images from Photoshop I’m left wondering if there isn’t an app like Swift 3D that has a plug-in that allows for quick generation of this effect.

Notice how the loader transitions into an animated page that twists and flips into place as the main stage. This is what I’d like to do, but after a long Google search and looking through more Flash tutorials on ‘animation’ than I’d like to admit I’m left wondering ‘how’d they do that’?

Anyone have a link to a tutorial or know a quick answer to help me sleep at night?