Sprint slashing the cost of Apple's iPhone 4S by $50 was seen by many as proof that the carrier is working to clear out inventory ahead of the handset's rumored successor. But apparently that was only the beginning: Sprint is now taking things one step further by throwing in a $100 gift card when you purchase and activate any iPhone 4S on a new line of service. This essentially brings the cost of the base 16GB model down to $50 when you factor in the bonus, with the 32GB and 64GB phones coming in at $149 and $249, respectively. Payment comes in the form of an American Express Rewards Card which Sprint says should arrive at your door between eight to ten weeks after buying the device,

To be clear, other smartphones in the carrier's lineup also qualify for the AmEx gift (including the Galaxy S III and HTC Evo 4G LTE), but this easily ranks among the cheapest ways yet to take home last year's iPhone model. Of course, don't forget about that monthly bill you'll be committing to as part of the deal; unlimited data doesn't come cheap.

Better still, Business Insider reports that Apple — already matching Sprint's $50 discount — will counter this latest offer with a $100 Apple Store gift card at its retail stores. But considering the AmEx card can be used in more situations (including shopping with Apple), that strikes us as the better option. Unfortunately the promotional period only runs through August 26th — well ahead of the new iPhone's expected public reveal. Still, if you'll positively be content with a 3.5-inch display for another two years, it might not be a bad way to go.