My girlfriend recently upgraded her connection from 15mb to 5.0 mb. She returned her cable modem because it wasn't capable of her new speed. We went to frys and picked up a surfboard sb6141. Everything is great except their is no voice over ip on that modem which she has with comcast. Do they have a separate voip box that would work with xfinity? We really don't want to return this new modem.
So you can use a separate emta, but your still paying the $7+/month rental fee for it, so it really does not make sense to do this. Some Best buys will sell the eMTa [phone + modem box], but its only a few here and there, and they are the only place that I know if that sells a VALID box for use with Comcast, whom I work for.
The additional issues comes with do you have the signal to add another split and keep both the modem and emta in spec for their services, this is basically a domino effect that is not going to be the easiest to accomplish unless she just plans to drop the phone soon.
Comcast voice service is strictly VOIP, the difference is it does not go across the internet, it stays on the CRAN [comcast regional area network, think fiber ring], so it is not like third party providers in that sence, the truth is its really not any better, I had vonage when the company wanted me to pay full price for CDV, when they switched to a $1 service cost, I picked it up becasue they were cheaper than vonage.
The sales pitch is we can do QoS on our network not the internet, but seriously I never had a problem with vonage unless I had problems with my internet. The whole packets arriving out of order scare tactic never was a problem.