The Windows Phone Developer Team had a twitter Q&A this evening, revealing a few things regarding the platform, discussed backwards compatibility, as well as a few other tidbits.
Learn more about the platform by reviewing the Q&A here:
Charlie Kindle has a great post as well on the Windows Phone Development Model:
I have been working closely with Microsoft Communications Business (MCB) and many of my customers for several months on Windows Phone and I am so excited to be able to talk publically about the new platform and capabilities at MIX 10. Come visit me in the Windows Phone booth on Tuesday and I’d be glad to answer your questions!