Alternately, if you are using OBiTalk (which is the easier way) to do setup, you can just tick the "Make This Service the Primary Line to Call Out From" box in the SP1: Google Voiceâ„¢ Account setup.
On your first post, you asked "can i buy the obi110 ...". So I figured you were at the pre-ordering stage rather than the implementation stage. That "Make This Service the Primary Line to Call Out From" selection would be pretty apparent during setup using OBiTalk, I would have thought. However I have an OBi202, so my suppositions about OBi110 setup may be flawed.