Nokia Lumia 800. The unknown model is shown twice in the video, once in the very beginning sitting on its side, and again at the very end. The idea of the video is to get developers to write for Nokia now that it has partnered with Microsoft. As the video notes, "Today the sun will rise and set, everything else is up for grabs".
As for the unknown Nokia smartphone, perhaps it is the Nokia Champagne that came up recently in the logs of the "I'm a WP7!" app. This phone, as we reported, is expected to run on the Tango version of Windows Phone. Tango is thought to be a stop gap version of Microsoft's mobile OS that will come in between the recent Mango update and the next major one.
When you check out the two videos below, the first one contains the mystery handset while the second one has the Nokia Lumia 800 as a replacement.
source: WPHone.nl (translated) via WMPoweruser