Go to your Google Voice web settings under phones (Settings/Phones). This is where you should see where your numbers are being forwarded to. Uncheck your cell phone as a forwarding number (your phone should not ring after this). Do you see "Google chat" as an option? If you do, click the forwarding box to include forwarding to Google Chat. This should then ring your OBi device.
If you don't see Google chat under the Phones section, let us know and we can further guide you.