Obitalk,
I think what you want is to block certain caller from calling your OBi unit at your google voice number, correct?
1. If you want to block ALL callers, you can set
your SP1/2 (where your GV account is configured) InboundCallRoute= (blank)
2. If you want to block just a few callers with specific phone number, say
14081234567 and 15109993333, set InboundCallRoute =
{(14081234567|15109993333):},{ph}
3. If you want to block anonymous callers (who do not want to show their caller-id number),
set InboundCallRoute = {?:},{ph}
4. If you want to block 800 and 900 callers, set
InboundCallRoute = {(1800xx.|1900xx.):},{ph}
5. You can do combinations of the above, such as
{(14081234567|15109993333|1800xx.|1900xx.)|?:},{ph}