I have often heard that charging a cell phone and calling in the same time may cause the cell phone to explode.
Here is a Facebook page that has pictures of what is claimed to be one such example. [Caution: pictures may be distressing and may not be safe-for-work.]
The French text that goes with the picture pretty much tells the story of a child answering his phone while it was charging. The text describes some unexpected symptoms that are a bit unexpected: he suffered a heart attack, his face changed color and he received a burnt hand .
If you just Google "cell phone charging danger", you will get many hits telling the same kind of story.
Can mobile phone explode if you use the phone and charge simultaneously?