Obi (phonepower) to GV and then use GV credit

I have a Obi100 and a google voice account. The Obi100 has Phonepower on SP1 and 'spoofs' the GV number on outgoing calls. The GV number is configured to ring the Phonepower number if anyone makes an incoming call to GV
I have some existing google voice credits in my account that i want to use to make international calls. i thought it would be as easy as using the Obi (phonepower) to make the call to my GV number and then use the credits to make international call. However, when I call the GV number, I get a long pause and a hear a message "number you dialled was rejected by service provider. reason code is 487". Any idea what I need to do to make the call from my Obi (phonepower) so that I can use my existing GV credits for international calls? Thanks in advance for any suggestion.