Before ordering a Volla phone I was sure I'd determined that it was compatible with local frequencies on the west coast of Canada (B5 on Koodo and telus, and B5 and B7 on telus) and I'm able to connect with either Koodo or telus (strong signal and either 4G or LTE). But I'm only able to send/receive text message and use internet (web browsing works). I can't send or receive phone calls. I upgraded to Android 10, and I compared phone info between my current phone, Google Pixel 4, and the Volla phone (using *#*#4636#*#* to get details). And I can see that data is "connected" and Voice is "in service". One difference I've noticed is that, by default, the "mobile measurement info" section shows LTE on my Pixel and GSM on the Volla phone. I experimented with changing the preferred network type on the Volla phone and was able to get "LTE" showing up in the "mobile measurement info", but it didn't seem to make any difference.
Also, the IMS status is "unregistered" on the Volla phone, and "registered" on the Pixel 4 (which gives Voice over LTE). So I'm guessing that this could be an issue with Voice over LTE not being available on the Volla phone.
I've spoken with Koodo and telus and went to a local company that specializes in telephony, and they all said that it should be working.
I don't understand cellular communications well enough to take this any further so I'm hoping that someone here can offer some suggestions.