Tom Keating has someone's tale of woe that sounds just dreadful about continuing to be billed after a phone number was ported away from Vonage. Ouch.
I went through a similar experience, but back in the day of Mad Dog Mike Slepian on the PR team some satisfaction was gained and after porting my number to Junction Networks (who are now a client). I had to pay the termination fee, but was credited for the months after I had moved the number and Vonage had stopped being the service provider.
Dear Andrew Abramson,
Your Vonage service has been cancelled and a final credit of ($65.00) was issued to your credit card on 07/13/2006.
Here's my take. The customer will eventually get their money back and Vonage gets one more black eye in the area of customer service.