I do understand your frustration, in the USA we have not had 3G or 2G since 2021 in most places and the lack of VoLTE support is why I had to leave Ubuntu Touch behind sadly.
But calls can be made with non-VoLTE capable phones using SIP or XMPP accounts such as jmp.chat in North America. You need cellular data of course, so after your carrier’s 2G/3G towers are gone that means 4G/5G, but even for older Samsung devices they support 4G LTE data (as does Ubuntu Touch 
).
So I have suggested that iodé add a big warning / disclaimer to the Samsung devices in the shop noting that VoLTE is not available on them with a brief but clear explanation of what that is (and even possibly link the sunset guide @Taurus-II linked so users can check if they don’t know what all of that means).