This trick only seems to work for the Obi110. It does not appear to work with the Obi20x series with obiline adapter. When Making a call through your POTS telephone service or when using a device like Magic Jack or nettalk Duo connected to an Obi110 you can spoof your Google Voice number by calling your Google Voice number dialing 2 and then dialing the number. On the Obi110 this can be automated.
In the following example you would replace 14195551212 with your Google Voice number. This was a simple proof of concept design. Improvements can be made but this is tested and working. You would want to make changes to properly route 911 and to cover other dialing patterns. This String requires direct no pin access to your GV account however it can be modified if using a pin.
Physical interfaces
>>>>>>>>>>>>>>Phone Port
>>>>>>>>>>>>>>>>>>>>>>>>OutboundCallRoute Set to the following
{(<14195551212,,,,,,,,,,2,,>1xxxxxxxxxx<#>):li}
Note: There is going to be a delay between dialing a number and the phone ringing. That is a necessary part of the process. You can adjust the number of commas in the string to decrease the delay but this is the minimum reliable number in my tests.