One of the nice things about Skype is the messages are encrypted, whereas the Vonage calls are in the clear, the second or so of lag is dependent on the speed of your connection and the computer plugged in.
Testing both, I like Skype, but having a phone number that follows you wherever you have a highspeed connection like Vonage is also great.
Nothing better than a week in London, with a Chicago number and your friends and business associates are calling you nearly for free.
