YEY! One more reason to love my Windows Mobile phone! Check this blog post (Conversations with the Communications Sector : Control PowerPoint Slide Shows with Windows Mobile) out. It shows how you can turn your Windows Mobile phone into a Windows Sideshow device. Find out more about Windows SideShow at http://www.microsoft.com/windows/windows-vista/features/sideshow.aspx
And yes, you can develop your own SideShow gadgets too! Check out the other sideshow gadgets at http://gallery.live.com/results.aspx?bt=8&pl=7
Developer resources on the Windows SideShow platform can be found at http://msdn.microsoft.com/en-us/library/ms744147.aspx