Google Voice classifies forwarding phone numbers as either "Home", "Work", or "Mobile". By default, forwarding phone numbers with type = mobile will be directly forwarded to Google Voice voicemail when you call your GV number. This is so that you can easily check your VM messages. If you instead want it to ring your GV number first, then log into your Google Voice account from a computer's web browser, not your cell phone, go to the Legacy web user interface, on the Phones tab of Settings, and click the Edit button under your cell phone number. On the next page, change the "Phone type" to "Work" or "Home" (landline). Click the Save button.
Now, when you call your GV number from your cell phone, it will ring any other forwarding numbers, plus Chat (your OBi acts as a Chat client). If you do want to listen to VM, touch * to barge into your greeting.