If you recently purchased an HTC One S for T-Mobile, congratulations - you've got one of the best Android phones available in the US at the moment. But as is usually the case with high-profile phone releases, there's at least one fly in the ointment. T-Mobile's unique WiFi calling service is included on their version of the One S to save picky customers from using up their calling minutes. But it looks like this feature is draining the battery unusually fast, and at least some T-Mobile customers must have already complained.