1) Open and sign into your Google gmail account associated with your Google Voice phone number {I use Google Chrome myself}.
2) Open a new tab in the browser and sign into the OBi Dashboard with your ObiTALK account user and password.
3) Click on the link to your Obi device.
4) Click the Settings Icon for the Service Provider SP Port.
5) Select Google Voice.
6) Verify and update settings for Google Voice.
7) Save and look for a POP-UP window with a list of your Google user accounts.
On the POP-UP, Select the Google user associated with your Google Voice Account and confirm.
ObiTalk will setup the Google Voice as a Service Provider.
The steps above are from memory and I'm sure that if I missed anything, someone else will be happy to assist with additional information.
Sorry for the Smiley in the reply, for some reason, I couldn't get rid of the smiley in the reply.