I'm thinking of replacing my current landline phone service with Xfiniity voice. However, I'd like to have my Xfinity voice service connected to the phone wiring in my house so that all of my existing phones will work. Is this as simple as plugging the phone wire from the modem into one of the phone outlets? If I can only have one phone on Xfinity or need to replace all my phones with a common wireless handset system, I'll probably stick with what I have.
You certainly can backfeed the Comcast Digital Voice eMTA telephony modem into your house wiring. The big caution is to make sure your inside wiring is disconnected at the Demarc (NID) from the local telco, and that it can't be reconnected.
For most installations, the eMTA plugs into a phone jack in the room the eMTA is located and if everything's wired right, all jacks should be active.
The other caution is for homes with alarm panels that dial out. The wiring of the eMTA throught the RJ31X jack must be done correctly or the panel will not have a dial tone.
There are several web sites showing pictures & diagrams with details by searching for "voip backfeeding".