The T-Mobile HTC Radar 4G was a bit of a surprise hit when it was released last October for a very fair price of just $99 with a 2 year contract. Now there’s an even better deal where you can get the phone for free, and T-Mobile will give you an extra $100 for your old phone. First off, the deal is only good through 1/5/2012 which is tomorrow. Secondly, it’s a web-only deal, so you’ll have to go to T-Mobile’s site to take advantage of it. Thirdly, you’ll want to make sure that your current phone qualifies for the $100 trade-in, which you can do by clicking here and entering “RADAR4G” as the promo code. Oh, you’ll also get a $25 gift card that you can use to buy apps for your phone in the Windows Phone Marketplace.