Phones can explode. It's not a common occurrence, and it is more likely to happen when a device is being misused in some way, but it's still not outside the realm of possibility for a device to harm someone who was using it precisely as intended. An 18-year-old woman in Switzerland was badly burned this week when a Samsung Galaxy S3 exploded in her pants pocket. The incident took place while the woman was at work, and her boss had to tear off her pants in order to help her.
Remember last month when an innocent user's Galaxy SIII was said to have spontaneously combusted? In the original post, user dillo2k10 told a harrowing tale, explaining that during a seemingly average drive, his S3 got a little too hot: