The Pocket Heat app is just 99 cents, so it's even cheaper than those throwaway chemical-based heat tablets you can jam in your gloves and socks. But of course it's not cheap at all in comparison to a new iPhone, so you might want to think this one through before you jump on the bandwagon and download it. Of course, if you're desperately addicted to your iPhone and carry it with you on the slopes anyway, this might be handy if worse comes to worse.
Here's a non-English video demoing the app (key point: his phone survives the test):