I have used Skype for a few years to keep my minutes down on my cell phone. Skype is not designed to take the place of regular phone service where Vonage is. You cannot call 911 from Skype but can from Vonage. At about $30.00 per year to make outgoing calls to the US and Canada without any special equipment except a microphone, which is built in with my laptop, I find Skype to fit my needs very well. Vonage is $300.00 per year which is 10 times the cost of Skype and the calls are always very clear. Of course there is the limitation of 10,000 minutes per month, but that has not been an issue for me.
My point is that comparing Skype to Vonage is like comparing apples to oranges. They are different services and each one has services some people need where the other one doesn't fit that persons needs. I am going to help my friend set up Vonage in a few days (I have a computer business) where they are changing from Qwest. Skype is made to suppliment whatever service you have, not to replace it.