If you don't find a solution, you can always configure the OBi directly by logging into it at the IP address returned by dialing ***1 (username/password is admin/admin):
Google Voice on SP1:
Service Providers -> ITSP Profile A -> General -> Name : Google Voice
Service Providers -> ITSP Profile A -> General -> SignalingProtocol : Google Voice
Service Providers -> ITSP Profile A -> General -> DigitMap:
(<1aaa>[2-9]xxxxxx|<1>[2-9]xxxxxxxxx|1xxxxxxxxxx|011xx.)
where aaa is your local area code.
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