Which model supports wifi call(VoWifi)

Hello.

I would like to know if there's any model that is not support wifi call?

I heard VoWifi(wifi call) is available over 6/6S. But is there any model after 6/6S that doesn't support wifi calling function?

One more question is...

Would it be any possibility that the wifi function of same models selling in different countries is different?

e.g. iphone 12 purchased in U.S. is wifi call available but iPhone 12 purchased in Hongkong is not available like this?

Thank you for your answer in advance.