I've been living with my Google Voice/Obihai system (see 1, 2, 3, 4, 5, 6, 7, 8, 9), for a couple of years and it continues to work great and for free!
Obihai sunset the OBi100 a while back and I upgraded to an OBi200. It took at least 2 minutes to make the transition.
Then in early 2018 Obihai was acquired by Polycom. Remember the old Polycom "Star" speaker phone?
There was one feature of Google Voice that wasn't supported by Obihai.
Google Voice has a call screening feature that will let you challenge a caller to identify themselves then ring your phone and announce the caller. At that point you can accept the call or send it to voice mail. While the caller is leaving a message, you can listen and pick up if you want to.
The Obihai system would challenge a caller to identify themselves but then immediately ring your phone without announcing the caller.
In practice that challenge caused most telemarketers to just hang up.
Then Google made a seemingly unrelated change to Google Voice. The result of that change is that now the screening works!