Hello.
Welcome to the Three Community.
I can confirm that all of the SIMs have the ability to allow WiFi calling on them. If the device has the option for WiFi calling, then generally it should work.
If the device allows additional WiFi calling options, such as Prefer WiFi calling, or Prefer Network, please choose the Prefer Network/Network Preferred option.
The only other thing I can think of going a little further back, and I'm not sure if this is still the case on phones today, but further back, some phones would have issues using features like WiFi calling or VoLTE if that phone was originally purchased from another network provider. This was because the provider had their own carrier software installed and it sometimes created issues with the configuration on other networks. I'm not sure if this applies to your phone or not.
It might be worth speaking to the manufacturer to get further advice in case there is a solution they can recommend if you're still having issues.
Pete.
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