Here are what I see. I am newbie to the VOIP

Beside you can connect to GV.

It has the following list that you can config.

Broadvoice

Callcentric

inPhonex

Sipgate

Google Voice

Vitelity

VoicePulse

viop.ms

GenericService Provider

 

I click on Callcentric. It goes to the Callcentric Account configuration page.

I compare it to Google Voice config page. It's slightly different. Same thing for other service providers. Some have proxy, some don't have.