[holo]

it's the excessive battery drain and charging, I get this often while using slingbox to stream video with it plugged in (without wifi even on), and the device simply gets too hot.... the solutions mentioned are good and maybe even just aim a fan at it and/or take off the battery cover....

also, prop it up so that the bottom of the phone is not touching a surface, especially fabric or something, as this will be very insulating....

I wouldn't worry about it exploding. The battery contains a circuit that will kill the battery if it gets into that temperature range. The phone will probably shut off before that happens anyways...

Note however, that heat especially while charging will reduce the life of the battery. While a couple of times is probably not a big deal, if you are overheating it daily, you'll probably significantly reduce the length of time your battery will last.....