My roomie ordered Vonage before consulting me the resident geek. He had it for a while now uninstalled because the modem is in my room and I told him he needed to ask Vonage for a solution to have a cordless phone connected in the OTHER rooms....
Vonage was unhelpful but I came up with a solution. We went out and bought a base phone with an additional handset. I connected the base and voila...the other hand set was ready to go and make and receive calls over the internet.
Another new solution I might get for myself is called Magicjack...it is about 20 bucks a year for unlimited calling throughout the US and canada through your internet. And I like it since there is no dumb modem to connect. You just connect a little USB device to your PC that is connected to the Net and plug in a phone. That's it
http://www.magicjack.com/6/index.asp