As the comments on that videos say, it's using VNC. The Windows Mobile phone is a VNC viewer, and the VNC server is running on a N900 or the Maemo SDK. Read up on the Wikipedia article and you'll understand how it's possible, and that it's not "MeeGo/Maemo running on that device". You can use x11vnc on the N900 or in the SDK to "export" the screen as VNC server and then you just have to find a VNC viewer for Windows Mobile and connect to the VNC server. This obviously also works on all platforms that have network connectivity and some VNC viewer implementation.