You won't be able to use Google Voice directly with your OBi. You already made the decision to purchase outgoing minutes with Callcentric, and you already have your OBi configured for Callcentric because you have one of their DIDs. So you can make outbound calls via Callcentric.
For incoming calls to your Google Voice number, just have them forwarded to your Callcentric DID. You do this on your Google Voice page. You can also have incoming calls dialed to your Callcentric DID if you give that number out to people.
Again, since your OBi can not communicate with Google Voice in either direction once XMPP is shut off, you may as well delete the SP for it in your OBi. It will be completely non-functional, you may as well remove it and free up an SP slot that you my want to use for other purposes.