Thanks for checking into this with us. It's a great question. There is indeed a way to guarantee your calls go out over WiFi. It works well in the US as well. You would place the phone in Airplane Mode and then turn on WiFi afterwards. If you turn WiFi on first, it will disconnect when you initiate Airplane Mode. While in Airplane mode with WiFi on, all your calls will go out over WiFi Calling. I hope this helps.