So I convinced my brother to buy the 521. He has been using an old Nokia flip phone for years and decided a phone held together by tape wasn't a good look. So he signed up for the $50 prepaid plan (unlimited txt, talk and 500mb of high speed data). One of the reasons he went with mobile was the WiFi calling. He calls me today telling me that a tmobile csr told him the WiFi calling doesn't come free with the plan (brother told me it was like another 7 bucks or so). Is this really true? I always thought it worked on any of their plans considering you are just using the minutes your plan comes with. I have never had tmobile so that was a guess on my part.