Connecting a Yealink SIP T54W to my Xfinity router/modum

I have Xfinity triple play. Right now I use an analog phone with my Xfinity land line phone number. I just bought a Yealink T54W VOIP phone and would like to connect it to my router and use my Xfinity telephone number on the new Yealink VOIP phone. It says "No Service" on the phone. It is WIFI Yealink phone and my iPhone connects perfectly through wireless. How can I get my YeaLink to work with my Xfinity phone number through my router?