In an industry where customer churn can be likened to the fearsome troll under the bridge, Sprint has launched a program designed to keep its favored subscribers around for another two years. While not everyone is eligible -- those who've upgraded less than eight months ago, corporate outfits and those in collections need not inquire -- the program lets customers buy their way out of their current commitment and become eligible for a new, subsidized handset. The promotion begins February 12th and is set to run through the 14th of March, where the amount you pay