This may have been a fairly big CES for Windows Phone, but it looks like Microsoft still has a fair bit of convincing to do in order to bring all the carriers fully on board. That includes Sprint, which does currently have a Windows Phone in its lineup (and is apparently considering more in the "August-September time period"), but remains decidedly unenthusiastic about the platform as a whole. As PCMag reports, Sprint's David Owens said that the carrier is willing to train its reps on Windows Phone, but that Microsoft has to "build the enthusiasm for the product," adding that the "number-one reason the product was returned was the user experience." Sprint's director of product development, Lois Fagan, further added that the carrier remains "cautiously optimistic," but that Windows Phone "just hasn't taken off." In other news, Owens also confirmed that Sprint would expectedly now be focusing all of its intention on its new LTE network, and not produce any more WiMAX-based phones -- although, as it's noted previously Sprint will continue to support the network itself through 2015.