Assuming the OBi is configured and working properly with SP1/ITSPA = Google Voice and SP2/ITSPB = VoIP, make the following changes:
Physical Interfaces -> PHONE Port -> PrimaryLine : SP1 Service
Service Providers -> ITSP Profile A -> General -> DigitMap :
(1xxxxxxxxxx|<**81>[2-9]xxxxxxxxx|<**81514>xxxxxxxS4|<**2>011xx.|xx.|(Mipd)|[^*]@@.)
If these changes are made locally instead of through the OBiTALK configuration facility, also change:
System Management -> Auto Provisioning -> Auto Provisioning -> Method : Disabled
NOTE: The ITSPA DigitMap above adds a leading '1' to any 'area code + number' being sent to the PSTN. If the '1' is not desired, change the two occurrences of '**81' to '**8'.