This is not "forking" in the context of a digit map in your OBi routing calls, nor is it an OBi issue. Google Voice is a call forwarding service. When someone calls your inbound Google Voice phone number,
Google Voice, not your OBi forwards the call to all of your check-marked, linked forwarding phone numbers, AND to the old Google Chat service. OBi devices are Google Chat clients.
Google Voice has an optional feature, known as call screening. When call screening is enabled, you will hear a prompt that says "call from xxx", where xxx is one of your Google contacts, or it will say "call from unknown caller" when the number is not in your contacts. It will then say "Press 1 to accept the call, or to press 2 to send the caller to voicemail".
You can disable that feature. Log onto your Google Voice account on a laptop/desktop computer, and go here:
https://voice.google.com/settingsHowever, note that this will cause a problem if you do not take additional steps: your linked phone number(s) (e.g. your cell phone number) must support Conditional Call Forwarding (CCF). When you enable CCF, your mobile phone network will forward all busy or unanswered calls back to your Google Voice voicemail box.
All of the "big four" US mobile phone carriers support CCF, but the commands to enable or disable it differ by carrier. Most of their subsidiary brands or their re-sellers (MVNOs like Tracfone, Straight Talk, MintSIM, H2O) do not.