This isn't the first attempt to bring solar power to iPhones. As you may remember, in May, Dexim brought us the DCA19 P-Flip, a solar-powered battery and dock for the iPhone 3G and 3GS. The most recent patent filed by Apple was on Touch Sensor Integrated Solar Panels on media players.
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While the next couple of iPhones may not incorporate solar cells, given the recent patent applications by Apple, it's intuitive to realize that the company is looking to put more and more devices on solar power and eventually include iPhones. According to the patent application for solar cells on portable devices, Apple would completely cover the device in a thin film layer of solar cells, even the display.
According to Gizmodo, Motorola has considered fusing solar cells with LCDs. This would make your device even more efficient, because no matter which way you had it oriented in the sun, it would always be harnessing the power of the sun.
If Apple can cover your iPod or other devices completely in solar panels, then surely they can make a highly efficient solar powered phone. If not, you could always get a a solar charging case.