Powercast featured a short video on their wireless sensors blog to show LEDs being powered from the RF energy harvested from an iPhone operating in 2G mode.  When the phone is called it is emitting enough RF energy to power the LEDs driven by Powercast’s RF energy harvesting technology and a simple dipole antenna tuned for the 900MHz ISM band.  We added the Powercast logo to the iPhone, but there is no Powercast technology inside.  The sound is a litte low so you might have to turn up the volume a little bit.