That is why I was wondering...when I do go exclusive using the obi and GV, can I be able to route phone calls to another number when the internet goes down.
Google Voice will route the caller to voicemail if you don't answer the call within 25 seconds for any reason. Google Voice doesn't offer a means to detect that your OBi is offline and route the call to an alternate number in that event. You can have Google Voice simultaneously ring additional numbers along with the OBi, but I can't think of any other option.