Samsung’s Galaxy S for Sprint, the Epic 4G, is now on sale.  The WiMAX-enabled smartphone is now available online and in Sprint stores, which open at 8AM today. The Epic 4G features a 1GHz Samsung Hummingbird processor, a slide-out full QWERTY keyboard, and a massive 4-inch Super AMOLED display. The Samsung Epic 4G costs $249.99 after a $100 mail-in-rebate, when purchased with a two-year Sprint service agreement.