I love writing these kinds of articles - mashing solar and mobile together. Check out Mobius's recharageable solar case for the iPhone. It's a case, battery, and a solar unit all in one.
An our of charge in the sun gives you an extra 30 minutes of data use, more than half hour of video, and nearly 2.5 hours of audio playback. Charge it up to its full capacity and you get 8 hours of data and audio use and 1.33 days of audio.
I can't think of a better device for mobile folks. You're using the sun's power to charge your device and on top of that, you are almost free. Almost no need to look for an outlet. I'm sitting here in my office, I can be charge my iPhone right now right under the sun.
This is where the future is headed. Even if Mobius or others came up with a case without the added battery pack, a case with just the solar panel would also suffice. Now, I don't know how the wear and tear of the battery inside the iPhone will be like but its definitely something I should mention. However, Apple has been using the latest and greatest so I reckon the iOS batteries can take some charging on the go without much degradation.
Furthermore, it's likely that mobile device makers like Apple, and certain I've heard this from Samsung, that they'll be incorporating solar charging screens in the future. More than that, universities are also on the path. UCLA engineers recently figured out a way on their own to use the LCD screen to charge and power the mobile device. And the UCLA screen charge the device using ambient light.
The mobile green future is here. Albeit, in a case but it's here. Now, we wait for the tech giants to integrate them. Until then, I think we can be satisfied with this Mobius solar charger.