You can now enrol on the UNITY Windows Store apps Beta here.
You can now enrol on the UNITY Windows Phone Beta here.
If you enrol in both the Unity 4 Windows Store apps and Windows Phone 8 apps beta programs, you can develop games for the entire Windows ecosystem. People around the world can play your games on computers running Windows XP/7/8, Windows RT tablets and Windows Phone 8 mobiles.
This is a BETA Programme?
Unity 4 Windows 8 and Phone 8 support has not yet reached maturity: UNITY are still working on performance optimizations. There are also bugs and some features missing. However, UNITY feel experienced developers can take advantage of this early technology and already ship games on Windows 8 and Windows Phone 8.
How can I publish my games to Windows Phone Store ?
You will be able to port your existing games to the Windows 8 and Windows Phone 8 apps platform using the Unity alpha/beta builds.
Please note that any project deployed with a trial license will be watermarked and not for commercial release. Developers who wish to publish their games on Windows 8 and Windows Phone Store using UNITY alpha/beta builds should contact the Unity Sales Department.
For more details on the UNITY Beta programme see http://blogs.unity3d.com/
How do I add specific Windows 8 features?
UNITY Windows 8 Plug-ins
Bitrave plugin beta: http://www.bitrave.com/unity-windows-8-plugins/ contact them for beta access
Prime31 plugins: http://prime31.com/plugins# contact them for beta access