I have just purchased a router/modem combo from a solutions store (Netgear C6300BD) and I can't get my Avaya phone to connect to make calls. I was using a different setup at the last place I lived but wondering if the router will even support a VOIP phone?
Here are some tips voipvoip have put together for getting VoIP phones to work on residential routers and gateways:
http://www.voipvoip.com/customer-care/voip-router.html
It all depends if your phone is setting up a VPN first - you might want to check the Netgear support forums - here is a recent thread about Avaya 9650 ip phones having issues with Netgear c7000-
https://community.netgear.com/t5/Cable-Modems-Routers/Netgear-c7000-wont-connect-to-my-Avaya-9650-ip-telephone/m-p/1045899#M2157
