You know, Etoile, there's VIOP and many are able to make phone call using a telephone over the internet via
Vonage - VoIP Internet Phone Service for Home, Business and International Calling: Vonage – A Better Way to Phone for Less or any particular company... so they require equipment in addition to modem to send and receive phone call.
Like hearing can do with
Skype official website – free download and free calls and internet calls or
Gizmo5 Mobile via their computer desktop and headphone or webcam(which has mic built in)
So videophone is basically like Vonage but Sorenson used a proxy number instead of real number like Vonage do.