Here is an interesting article from PC Magazine talking about how sound waves can provide electricity.
Dr. Sang-Woo Kim and his colleagues at Sungkyunkwan University’s Institute of Nanotechnology in Seoul say they have developed a new method of converting sound into electricity. They say a cell phone could be charged simply by talking into it while other applications could include installing “sound-insulating walls near highways that generate electricity from the sound of passing vehicles.”
This will be interesting if they can get this working more efficiently later on. Then the possiblities – not just highways, but movie theaters and stadiums and any where else there is lots of noise. And as the article says, just talking charging your cell phone would be interesting.