Two-thirds of WiMax operators plan to use WiMax for mobile broadband by 2012. 90 percent expect to offer Voice over IP using their WiMax-based networks by then. A lack of smartphones that support the wireless technology will make it a challenge, according to a survey. The incentive for smartphone makers to adopt WiMax should grow as the number of potential users goes up, the survey says. Sprint’s launch of the HTC Evo 4G shows that there is a pent-up demand for smartphones on WiMax networks.”]