cdcooker,
By the time the OBi AA picks up the incoming call, and presents the caller with Options 1,2,3, the call is considered "answered", and therefore subsequently Google will not try to attempt to forward the call to voice mail. The 2nd ringing tone heard by the caller after he selects option 1, is generated by the OBi device, not Google, which have no idea the phone is ringing.
I don't really have a solution for this case, but 2 suggestions come to mind:
1. If the caller (in the circle-of-trust) knows ahead of time that he wants to ring the phone instead of
invoking AA, he can a) block his caller-id (by dialing *67 first on a cell phone, for example), or b) call from
another phone line/service that is not in circle-of-trust,
2. Replace your OBi phone with one that has an answering machine, as a backup VM for this case
Hope this help. Thank you.