You might try the following:
1. Delete the OBi from the OBiTALK Web Portal Dashboard (do not re-add it).
2. Disable your Internet connection (turn off your modem or unplug the phone line/cable connection).
3. Log into the OBi directly and reset it to factory defaults:
System Management -> Device Update -> Reset Configuration -> Press Reset to Start Process -> Reset
4. After the OBi reboots, log back into the OBi directly and set:
System Management -> Auto Provisioning -> ITSP Provisioning -> Method : Disabled
System Management -> Auto Provisioning -> OBiTALK Provisioning -> Method : Disabled
Service Providers -> ITSP Profile A -> General -> Name : Google Voice
Service Providers -> ITSP Profile A -> General -> SignalingProtocol : Google Voice
Voice Services -> SP1 Service -> AuthUserName : (Google Voice username)
Voice Services -> SP1 Service -> AuthPassword : (Google Voice password)
Voice Services -> SP1 Service -> X_SkipCallScreening : (checked)
Physical Interfaces -> PHONE Port -> PrimaryLine : SP1 Service
Remember to click Submit at the bottom of any page you make changes to.
Click Reboot in the upper right corner after all changes have been made.
5. After the OBi reboots, enable your Internet connection.