Charge your phone by walking - reverse electrowetting shows promising results1
They used 150 droplets arranged in-between multiple layers of thin film, which generate electricity when pressed upon and moving around. So far this setup has netted only a few milliwatts of power, but a few thousand of those together could generate enough power to juice up our gadgets, including cell phones.
While there is still a lot of work to be done to refine the technology, the practical take is that those few thousand droplets that are needed to plug in your cell phone can fit in a small patch about six square inches.
Hope they also find a way for the USB cable plugged in your Nikes to look cool, or else we'll have to take the technology that charges the phone from the noise around you, or your constant yapping on it.