What's WiFi calling and how exactly does it work?
Can I, for example, call another person over the office WiFi when we're both using the same WiFi network?
Maybe ASUS have not announce it in your country, just like our country.
If you want to use WiFi calling, you can dial #*#3642623344#*# , WiFi calling option will be appear in phone / setting, but you need to do it again when you restart you phone.
WiFi calling (if support has been added for your carrier) will allow you to call and receive calls to any phone via your wifi. It shouldn't matter which wifi you're on unless it has been deliberately restricted on that network.
Most carriers do not support wifi calling for ZenFone 6 but we have one or two in India. Can't remember which ones. If you have support with your carrier, then you will see a small status symbol with a phone that has a wifi signal over it.