These are all predictions of what Wi-Fi calling will look like on PM. Not fully true... yet!
Also note: neither TELUS or Koodo currently have WI-Fi calling outside of Canada... sucks. It'll be nice to have it in Canada because the US cellular infrastructure is way better there (mmWave, 5G SA, etc.)
Have it work internationally, but only for receiving SMS texts for 2FA verification. Otherwise when sending an SMS won't send or a call incoming will put it to voicemail, if you try to make a call it will probably say 'Public Mobile here, you cannot make Wi-Fi calls outside of Canada or the United States without an add on' then it will fail to call.
No US roaming add-on? No Wi-Fi calling. It may say 'Public Mobile here, you do not currently have a U.S. roaming add-on to make a call. Dial *611 or go to myaccount.publicmobile.ca to purchase a US roaming add-on.' Then it will fail to complete the call.
If you are currently using a VPN and Public Mobile knows that you are using it but cannot disable it, they may say 'Public Mobile here, we cannot complete your call since you are currently using a Virtual Private Network. Please disable the VPN and try the call again' Then it'll fail to complete the call.
It is somewhat of what Koodo & Telus use at the moment.
Otherwise, it will work normally in Canada or in the US with a roaming add on.
A little reddit comment from the Public Mobile reddit backs this up a bit with CS_Agent comfirmation