The idea of solar power in an iPhone is interesting. I have a Solio charger for mine, and it's great for keeping my iPhone charged on long hikes. I'm skeptical about the utility of having solar cells built into the iPhone itself though, because how often are people going to leave their iPhones sitting unperturbed in direct sunlight for several hours? Perhaps this will be more geared toward prolonging battery life by a small amount rather than being marketed as a full-fledged charging solution. I can see Apple selling this solution as a way to get an extra hour or two of life out of your iPhone every day, but using the sun as the iPhone's only power source will be more difficult, particularly if you live somewhere that doesn't get a whole lot of sunlight.
The concept is fascinating at any rate, and may be something we see in the 2011 models of Apple's portables.