So if you only have one sim card in it, the wifi calling works automatically and if you have 2 in it then it no longer works?
Did I understand that correctly?
I may not fully understand the question, but I'll try to answer. Wifi calling works for me in all cases, even if I have two SIM cards in it. The main thing is that I am connected to Wifi.
Wifi calling has nothing to do with the SIM cards, only whether I have a hotspot and whether it is then enabled for making calls.
However, if a call (e.g.) Whatsapp is made, then with 2 SIM cards you must decide in advance in the SIM card menu which SIM card is to be defined for data roaming etc. and which card will then only have 2G (phone calls).
Best regards
As mentioned above by "Grossnik", the one or two SIMs have nothing to do with WiFi these are two different and independent communication channels. Having said that the on-going call via GSM/3G/LTE will NOT be switched over to use WiFi in any case and this is regardless of how many SIMs you have installed in the phone.
If you have a better WiFi signal in a cellar then the GSM signal, use e.g. "Google Hangouts", Skype, WhatsApp, Viber or any other Audio call application available via Google Play.
Hope this helps.
