Yes. Cable modems can have an optional, built-in VoIP function, that is controlled by your cable company to provide telephone service. In your case, instead of using the cable modem's own VoIP function, you are connecting an external VoIP adapter (the OBi box), and the router simply sees it as yet another TCP/IP client on your network. Instead of getting telephone service from the cable company, you will sign up with Google Voice, or a SIP VoIP service provider.