I have just set up a VOIP service with Optus. I have a SagemCom F@st 3864OP modem and wondered if I could connect a Cisco SPA504G phone to it. The phone doesn't appear to have an RJ11 port to connect with the phone port on the router. When the phone is connected to an ethernet port it shows the correct IP address. Is it possible to connect via ethernet? New to VOIP.
I would say the VOIP service is attached to your modem. Dont think Optus supports BYO VOIP devices as Optus does not gives you the VOIP login details.
Look for a RJ11 port on the modem and connect a standard telephone to it.
if you search hard enough there are some guides to look for the VOIP details and use your own VOIP devices ... Do so at your own risk.