@Yummy You can also check if VoLTE is enabled on an Android phone by looking for the IMS registration, try something like Settings > About Phone > Status > SIM Status and look for VoLTE/IMS registration.
Your phone can be LTE capable without being VoLTE capable/enabled. I have one such myself, it is supposedly capable but was not enabled on my previous (Tier 1) carrier. It would show LTE in the status at the top but the LTE would change to 3G on voice calls. VoLTE is voice over LTE, it does not necessarily follow that a phone capable of LTE is also enabled/capable of VoLTE.
Your test suggests to me that the phones are not VoLTE enabled (as well as being used synonymously with LTE in many cases, 4G can refer to a kind of 3G I believe, depending on carrier, but someone more technical than me would need to comment on that aspect).
SMS should still work after the Canadian 3G shutdown I would assume, the carriers have ways to send them without 3G. Think about the USA which shut down 3G in 2022. People there are still able to use SMS.
