That'll cost you a penalty of at least 10% for cashing in before you're 59. Add the taxes Uncle Sam collects and you've already lost a sizable chunk of your savings. If you're between jobs, use this as a last resort — it will sting in the long run.
Cell phone companies tack on enormous fees — upwards of $150 in many cases — to discourage customers from terminating their contracts early. So if you're feeling the lure of the iPhone siren song, hang tight. The iPhone will still be there once your contract expires, and you'll have saved a big wad of cash.