Here is the response I got from them a week or so ago:
We're not sure if/when we will allow older ATAs to be attached to RingTo. Per our FAQ, we are not positioned to support every Obi device already in circulation at no cost.
This service with Anveo 911 added seems like it would have been the perfect replacement for Google Voice if it had come along at the first of the year before so many people moved to other services, though it has some of the same limitations, such as no CANM or MWI. Actually, MWI is working perfectly in my GV account at the moment. It's no frills, but that was the beauty of free GV calling. You accepted that you didn't get everything, because it was/is free.
My feeling after watching Google drop projects over time is just when we think GV free calling using an OBi is not going away, it will be gone.