I have Vonage with a road runner cable modem and I've never had a problem. I love it. The only thing I would say negative about Vonage is that Erik was having probelms with it for a bit and the tech suppport was in India and was VERY frustrating.

If you decide to go with Vonage, send me your e-mail address. If I refer a friend, I get two months free and you get your first month free.