The Obihai boxes (I have one which I use for Google Voice) use XMPP for Google Voice.
Google is killing XMPP support and the Obi boxes will no longer directly support Google Voice at that point.
Fortunately, the Obi boxes also do standard SIP. You can get a SIP account from a VOIP provider and a DID. Point your Google Voice number at the DID and you'll get incoming calls.
For outgoing calls, most decent VOIP providers will allow you to set your outgoing caller ID after verifying that the number is valid.
It's not free, but it works and it's relatively inexpensive.