These waves come from weak TV, radio, and mobile phone signals surrounding us. The power harvested is very small, but is enough to allow the phone to stay in standby mode indefinitely without needing to be plugged in.
The trick is that Nokia has devised a phone that uses circuits needing less power than it is able to harvest from radio waves. The goal is 50 milliwatts, enough to charge the battery slowly. The phone could be on the market in three to five years.