Hello - I have a samsung s7 which I purchased from 02 and I had an o2 SIM. At the time I was able to use wifi calling on my BT broadband through my o2 account which was very useful in a rural area with a poor signal in the house. I then moved over to BT mobile with the same phone ( Samsung S7) and installed the BT SIM. However, after installation of the BT SIM the wifi calling disappeared as an option from the phone settings of the S7. The BT helpdesk have told me that although WIFI calling is available with the S7 it isn't for phones that originated from another supplier, i.e. 02. Is there a way I can get wifi calling on my S7 with a BT SIM?
It may be worth your while searching Samsung help forum for the #* number code to enter on your keypad to re-enable wifi calling. I did this for my xiaomi mi 9t which now works a treat though not listed as a supported phone. Hope this helps