In order for the OBi device to answer the incoming G-Talk call with the OBi Attendant, you need to put the caller's Gmail user name in the "Phone Number" field of the OBiTALK Trusted Callers listing.
When GTalk-caller places a call to their OBi "buddy" from Google Talk, the OBi device will answer the call with its OBi Attendant. The caller will then have the choice to use their pc's keyboard to press:
1 to Continue the call - i.e. Ring the attached phone.
2 to Make a new call - Dial with the pc keyboard a regular telephone number followed by the #.
3 to Enter a Callback Number - Dial with the pc keyboard a number that the OBi will use to make the call back call.