Recently saw the Brookstone Pocket Projector for iPhone 4 on display in a Brookstone store. The Iphone 4 slips into a 2100 mah battery pack which resembled a Mophie Juice Pack with a miniature DLP projection system built in, capable of about 15 Lumens. The store unfortunately was brightly lit and no real surface to demo it on. The clerk projected it off two chairs and I could see that the video would have looked acceptable in a dark lit room. The spec claims up to 50 inch, however it has a resolution of 640 x 360 pixels so its something to keep in mind if projecting a large 50inch screen at 15 lumens. On the other hand when going for even 12 to 24 inch would be huge compared to a 4 inch iPhone screen and still look reasonably sharp. There is a built in .5 watt speaker, one would be better off using a blue tooth enabled Jam Box or similar device for more amplification though.
The neat thing is someone that is used to walking around with a Mophie Juice Pack or similar pack could basically replace it with this device and still have backup capability of a battery plus have a minature projector available at the flip of a switch (actually holding down a button for about 3 seconds) with almost no noticeable difference in size.