There's tonnes of news, photos, etc floating around the interwebs today about Microsoft's Windows Phone 7.
There's a big difference between WP7, iOS, Android and Blackberry - which by this video, is quite obvious from the start. The latter mobile OS's generally have a desktop with icons, where Windows Phone 7 is a completely different experience. It opens up with dynamic tiles which update with changing content from the phones app's.
The idea is that, all of the info is not hidden inside the apps, but displayed directly on the first screen you see.
Below is a video, demonstrating the UI: