Have a Samsung S9 with Wi-Fi Calling switched on.
The phone has an ALDI Sim Card, Aldi does Not have VOIP,
BUT
To me I should be able to link to my Telstra NBN Modem(or Telstra MF910 modem when out in the Bush) with the Telstra modem being my preferred Internet access in the S9 to use for Wi-fi calling.
And with reference to a Goggle query below: My phone is connected to the internet as it receives the weather etc
And In Connections Screen , Wi-Fi references my NBN Connection and Wi-Fi Calling is switched on.

But If making a call I do not get "Internet Call" or "Wi-Fi calling" on the screen.

What am I not doing?

TIA
Peter

Google Query
Place a call using Wi-Fi:
Once you’ve set up Wi-Fi calling, you can make a call over Wi-Fi just like any other call. When you’re connected to the internet, you’ll see "Internet Call" or "Wi-Fi calling" on the notification screen.

When you're not connected to Wi-Fi, your calls will use your mobile carrier, if you have one.