I'm having the same problem.
- Obi200
- Google Voice with
- Call Screening enabled
- Ask unknown callers to say their name
- Caller ID - Display caller's number
- Do Not Disturb - not checked
- Missed Calls - checked
- Call Options - not checked
- Global Spam Filtering - checked
For unknown calls that get through, we hear "Press 1 to answer call" and when we do, nothing happens and we can't answer the call.