I love the WiFi Calling feature. It really puts Fido ahead of the other carriers.
However, there is an issue while roaming on AT&T if WiFi calling is enabled. After a short period my iPhone 6S will go to No Service. If I do a network scan the result returned is 'Unable to load network list.' Toggling airplane mode will not change things and the phone must be power cycled. Of course it will soon go back to No Service so WiFi Calling must be disabled before power cycling.
This issue does not occur with roaming on T-Mobile. So an interim workaround is to 1.Turn off WiFi calling before entering the USA. 2. Manually select T-Mobile when in range. 3. Turn WiFi calling back on.
**edited to add labels**