Windows Phone 8, codenamed Apollo, will be based on the Windows 8 kernel and not on Windows CE as are current versions. This will not impact app compatibility: Microsoft expects to have over 100,000 Windows Phone 7.5-compatible apps available by the time WP8 launches, and they will all work fine on this new OS
Go ahead and read the whole thing, nice preview from Paul Thurrott on the future mobile OS from Redmond. With WP7 of to a good start, the future WP8 should have a solid foundation to build upon, especially since it will run all the apps available on the Windows marketplace for phones. This is something to watch for this year.