Sprint is launching its WiMAX, wireless service in Austin and San Antonio today, the firm said today. Sprint 4G is Sprint's wireless data service, which leverages the WiMAX data network of Clearwire. The firm said that Sprint Customers can buy a dual-mode, 3G/4G device for free after $50 rebate and a two year agreement, and will charge around $69.99 a month for unlimited 4G. Sprint is 51 percent owner of Clearwire, which is rolling out a nationwide, WiMAX network.