These things definitely have the energy to do serious damage.
My wife and I once started writing a techno-thriller based on having the bad guy distribute a new battery technology that had a timebomb embedded in the controller chip. It would have caused every cell and laptop in the US to melt down at the same time. Since most c3ells are carried in pockets, the eff3ect was to totally overload the emergency response while simultaneously knocking out communications.
Unfortunately, this was about the time she got really sick, and the project was never completed. I'm better at plotting and organizing, but she was much better at narrative and dialog.
Based on the number of reported incidents vs. the number of iPhone 3GS units sold your chances of having this happen are about the same as your chances of getting hit by lightening.