The Pocket Projector Case is a smartphone case with built-in projector and also includes a 2,100mAH battery, as well as a 0.5 watt speaker. Designed specifically for the iPhone 4 (but also conveniently compatible for the iPhone 4S), the phone slides into the case and engages the dock connector. From here you can project anything projectable onto a 50" rectangle on the wall.
50" is optimistic, however, and will require a pretty dark room to be accomplished. Brookstone's projector case also puts out a max of 15 lumens, which is the same amount as Microvision's SHOWWX+ pico projector. If you want an image that is bigger than a small television, you are going to have to turn out the lights. But isn't that kind of the point when you use a projector for entertainment?
The display has a resolution of 640 x 360 and the case's internal battery should keep it going for at least a couple of hours. In addition to that, the device can work as a backup battery for the iPhone within. One thing of interest to point out is that the case has a manual focusing dial, unlike the "infinite focus" of laser projectors. But that is to be expected for the relatively low price of $230.
Source: Wired - Pocket Projector: A Magic Lantern in an iPhone Case