I'm with Voyager (well, a legacy Actrix account...). A while back I purchased a Synology rt2600ac router to replace the pretty basic netcomm one that the ISP provided. I chose the synology because of good reviews and that it apparently supports VoIP.
When I tried to set-up the VoIP, Actrix told me at the time that they don't support VoIP on my router - i.e. they didn't have a guide on how to set it up and/or it wasn't compatible. So I used the router in Wireless AP mode, and everything was OK.
At the start of lockdown, my netcomm modem packed-up. I contacted Voyager and asked again about VoIP, and they said that it was "unsupported" on my modem. Given that my wife and I were both working-from-home, I didn't want to muck around with trying to make it work or change ISPs, but now we're back at work, I have more options.
Has anyone managed to get VoIP working on the rt2600ac with a New Zealand ISP? Looking through the various router settings, it looks like the VoIP can be configured and assigned to a given WAN point, providing the VID (and priority). Given that there is no other settings assignable here, I am assuming that either it is only "partial" support for VoIP, or it requires that the other settings (username and password etc) for the VoIP need to match those for the Internet service. With Actrix, they don't.
I'm no expert on any of this, so a bit of the above is guesswork.
Any support / information / feedback gratefully received!