One of the knocks against AT&T CallVantage was that it doesn't work behind your existing home router/firewall. Their nemesis, Vonage, is able to handle being behind or in front of a firewall - a huge competitive advantage, especially for the security-conscious techies that don't like having any device in the front of the firewall.
Well, Andy Abramson brought to my attention that this is no longer the case - AT&T CallVantage does indeed support being connected behind a firewall, as confirmed by this AT&T CallVantage How To link: AT&T CallVantage
Though I did read somewhere else that contradicts this and it stated that AT&T DOES NOT support having the telephone adaptor (TA) behind the router/firewall, but that they "will soon support such a configuration".
I guess AT&T is moving so fast to add features and functionality to CallVantage the left hand doesn't know what the right hand is doing!