Somebody better with the mathematics than I am will be able to calculate just for how long a mobile phone battery would be able to shine a projected image of sufficient brightness over a 300 sq in. surface. Not very long, is my guess.

I'd like to carry a mobile with that thing. Even 5 seconds should be enough to show off!...

If you could run it off a normal charger, I can see some huge benefits:

For roadwarriors, there are gadgets that can connect your phone to a projector (like Irma) and are powered by the charger. If a phone charger provides enough juice, then you would only need your handset in the future.

For media junkies, you would have the option of viewing your media on the phone's screen, or by projecting it somewhere using only a charger and your phone (rather than e.g. a much larger & heavier laptop.

Sounds like win-win to me!