Try the following:
1. On your dashboard at
obitalk.com, click the light blue gearwheel icon at the right hand end of the line for your OBi.
2. Click the light blue gearwheel icon at the right hand end of the line for the SP that has Google Voice.
3. Heed the text opposite "Replace Google Account Credentials" and click the link therein.
4. Follow the instructions.