Vonage now offers Click-2-Call service which allows one to automatically dial numbers from their computer:
With Vonage Click-2-CallSM, you select a phone number from anywhere on your computer and we dial it instantly. Click-2-CallSM rings your Vonage number first. When you pick up your phone, it then rings the number you picked to dial. You will be able to ring any number, in any location, on any device, without even dialing the number.
This sounds like a great feature. Sadly, it only available on the Windows platform. How about a web interface Vonage?