Use the Silverlight gateway on Sipsorcery to do the following steps.
Step 1
Create a ruby dial plan named default on Sipsorcery. Paste the following.
case req.URI.User
when /^00/ then sys.Dial("cheapintlcalls")
else sys.Dial("MyGoogleVoice")
end
Step 2
Add a Sip provider named MyGoogleVoice
Select Google Voice.
Enter your full email Google Voice email address as the user name.
Enter your Google Voice Password. 2-step verification must not be turned on. App specific passwords won't work.
Enter your Callcentric number as the callback number.
Select Home for the phone type.
Step 3
Create a sip account. This is the sip account you will use on you obi. Out dial plan = default.
Step 4
Go to callcentric and create this call treatment.
Call coming from Caller ID:
This number: = your google voice number
Redirect call to:One destination
This number:=
yousipaccount@sipsorcery.com The sip account you created in step 3.
Step 5
Set up a Gateway on your Obi.
AccessNumber = SP2(sipsorcery.com)
AuthUserID = The Sipsorcery user name the part before the @ sign in the sip address from step 3
AuthPassword = The Sipsorcery password for the sip account in step 3
Step 6
Set up a dial plan on your Obi to make use of the Gateway in whatever fashion you plan to use it. Do you want to use it as a backup? as you primary? As a fallback?
Outgoing calls using the Gateway go through Sipsorcery.
Incoming calls bypass Sipsorcery entirely.
If you want to use it as a failover you will need to create a trunk Group.
Trunk Group 1 = SP1,VGx where x = the Gateway you set up for Sip sorcery.
I don't know what your current dial plan looks like but you would replace sp1() with TG1() in your outbound plan.
With the Above setup if Callcentric went down Sipsorcery would not work. An alternative would be to use an IPkall number as a Google Voice forwarding phone. In Google Voice you would leave it unchecked and on the IpKall website you would forward directly to the sipsorcery sip account listed in step 3.
If anyone sees any errors let me know. I was very frustrated writing this because I accidentally closed the tab the first time I wrote it and I lost the whole thing.