I'm on iOS 9 with an iPhone 6 Plus I purchased from AT&T, but I'm now using with T-Mobile. I have been using Wi-Fi Calling since iOS 8. I want to enable Wi-Fi Calling Continuity, but tapping the button does nothing. I can use my iPad to make calls when my iPhone is on Wi-Fi calling when nearby, but I cannot be away from my iPhone and have it work. Does this "Add Wi-Fi Calling For Other Devices" button work for anyone else? I tap it and nothing happens. I did get a carrier settings update today to T-Mobile 21.1. I was hoping that would fix it, but no dice. Anybody else have luck? Photo of what I'm talking about is attached.