I’ve been working on this as I use an Obi202. I was able to get the Obi202 configured to call HA and the entities show up, but it looks like the VOIP integration today only supports the newer OPUS codec, not any other SIP standard codecs, so it isn’t working.
I’m hoping they will support older codecs (G711U, G771A, G729) which will enable a TON of existing ATA devices (and straight up SIP clients) to work.
I have opened a feature request, please engage there! https://community.home-assistant.io/t/support-for-other-codecs-in-voip-integration/568580