Hi Kobi,
Yes, I believe you are correct. While it should work either way, I would certainly try changing the Voicemail Access to Yes under the GV Settings -> Phones -> Google Chat -> Edit. See if that makes any difference.
Do you know if the number porting process has completely finished? I think you said things were working, but I just wondered if you place a call to your GV number from your Callcentric SP2 account, does it go through properly?
Hope you get this fixed!
pc44