I have a new 6s (iOS 9.0.2) with T-Mobile Wi-Fi Calling enabled and working. I can dial calls manually with no problem. But if I try "Hey, Siri, call Jack's mobile", it displays the correct phone number but then says "There's no connection. Try again when you have a better connection." Immediately after that, I can manually dial the same number and it works fine. (I have Wi-Fi signal but no cell reception at this location.) Apple Support's only suggestion was to wipe the phone and reload everything.