If there really is a market for an extension moniter like you suggest, it would be very easy to build. I don't think I've ever heard anybody suggest this idea before.

I didn't know cell-phones could play movies. I'm sure you could use a personal DVD player--which is about the size you indicate--but I guess you're getting your movies off of the internet using Wi-FI? Could you use a laptop.

I usually read or people-watch, so I'm not the intended market.

In Japan about 25 percent of youth in the age group 25-35 watchtheir favorite tv channels on their cell phones, with speeds going upto4 gbs. In Indian most of the popular TV channels are available forthe cellphone users. Watching movies on a laptop may be cumbersome.A small monitor with a 4-5 inch monitor can be placed at a vantagepoint so that you don't strain yourself much, when watching a movie.The monitor could also be bluetoothed so that you have a wirelessmonitor.

i think this is a great idea, with the current cell capabilities of video, high res images, games, and GPS having a larger screen available would be great. I think the same is true of devices like palm and pocket pc's, I would gladly pay for a 5" screen for my phone or other devices. especially since it could easily be produced and sold for $100-$150.