If you use Vonage, and you want to be able to make calls from your PC instead of an ordinary telephone, you need what is called a “softphone” client, a piece of software that connects to your Vonage account and dials into the public phone network. You will also need to upgrade your Vonage account with a $10 a month optional softphone feature.
The Windows softphone works reasonably well, but the Mac version is the pits. Over the past couple of months, I have tried a variety of other clients, finally settling on the is-phone Portable version. In theory, any SIP-phone should work, but you’ll need some combination of parameters and configuration help files are very sparse when it comes to setting things up with Vonage. Here is a screen grab that shows you how I did it. Note, you have to use the softphone password which is different than your Vonage account password, and there are some other special settings too.