3DBoard provides the iOS 7 3D effect on a jailbroken iOS 6 iPhone
http://www.youtube.com/watch?v=krEGXx70SUY
If you’ve jailbroken your iPhone, you don’t have to wait for iOS 7 to get the 3D parallax effect – you can download 3DBoard from Cydia.
As you’d expect, it doesn’t look as polished as the iOS 7 effect, but if you just have to have the effect now …