To all,
I had the same problem stated in this thread. I know for sure that I did not have this problem 5 days ago, however, I don't know when this problem started as I just noticed today, which is when I started looking at the forum for a resolution. I tried a few of the suggestions on here (e.g. upgrade the f/w, reset the OBi, disconnect then reconnect GV from forwarding to Google Chat), but nothing worked.
Here is what solved the problem for me. Hopefully this resolves it for others also.
Assuming Google Voice is your Profile A,
Make sure Service Providers -> ITSP Profile A -> RTP -> X_UseSSL is unchecked.
I was checked in my configuration, and I believe it was always that way when it worked fine, but now only when it is unchecked can I successfully make inbound/outbound calls.