I have had my GS5 for about three weeks and love it, but I cannot send SMS via Wifi. Is this an AT&T problem? An issue with my phone? Or do I need a different texting app/platform? Some forums suggest turning off Wifi Calling in Settings/More Networks, but that selection is not available in mine. Others have suggested AT&T and other companies are trying to suppress the feature. Does anyone out there have a definitive answer one way or the other?