When i get anti incoming call WiFi, it rings 3 or 4 times and then does not go to voice mail. It just says I am not available and to retry later. It works fine with normal incoming calls. I have tried safe mode to see if any app was causing it but it was the same. All you can do with WiFi calling is turn it off or on, there are no settings I can find. The mmi codes all truth invalid network response.