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.
