Great question.
Briefly put, I have two answers that take me in different directions.
1) The Advertising Agency Version: show practical functionality that relates to what people do in the day - easily, and fast - BUT - a) make the "functionality choices" revolve around segmented target market needs - and - b) make the ads appeal to people's sub-culture affinities.
2) The Information Only version: I always feel a straight informational ad, while artistically boring, can convey a lot of practical information that prospective users can sort out. Imagine some a voice-over that goes something like this:
Hi. You may have noticed that many phones today come running Windows. In fact xx companies (images of corporate logos) are making over xxx diferent types of phones (images of various latest phones), all running Windows Mobile (zoom in on typical Homescreen). All the major phone companies around the world (logos from around the world) offer their customers (smiling faces of all races, cultures) Windows Mobile phones so they can do al sorts of cool things... like (and here is the listing of things you can do with corresponding images of phones doing these things) making voice activated calls, sending txt and email mesages, taking pictures, listing to the radio, listing to their personal music collections wirelesslessly with Bluetooth headphones, surfing the web, getting through traffic and planning trips, finding movies, playing games, record music, edit movies...etc... If you'd like to know more about if Windows Mobile phones are right for you, check out WindowsMobile.com and see how Windows Mobile can fit your lifestyle.
I'm not a copywriter, but the idea I suggest is to, in plain spoken language and demonstrations, show what can be done.