Hidden away in the Vonage Alpha Labs is the "Vonage Talk" application.

This all-in-one call/IM client is not the same thing as their existing V-phone product, and apparently it works with ANY Vonage account. I tried it myself, and calls go through instantly and clearly.

Audio is supported through any Windows audio device, so you should even be able to use a Bluetooth headset (if correctly paired to your PC).

The application also has support for MSN, Yahoo, AIM and Google Talk instant messaging clients.

I’m extremely impressed with it, it’s released as open source, and it is free of charge for any Vonage customer.

Vonage Talk allows a Vonage customer to enjoy Vonage’s world-class phone service through their PC. Vonage Talk provides an intuitive, easy-to-use interface to meet all your communication needs. Place calls, receive calls, and pick up your voicemail too.

In addition to making calls, Vonage Talk allows you to chat with your friends while logged into all of your IM accounts at once including AIM, MSN, Yahoo, and Google Talk. Best of all, Vonage Talk is included at no extra charge and calls made using this feature enjoy the same great rates as your other Vonage calls.

Every great inventor has their own special way to keep track of great ideas. Here at Vonage, we put our great ideas into practice. You can even help us make them better by letting us know what you think. Step inside and play awhile.
Vonage: creative minds making the voice over network age…timeless. Go ahead… experience Vonage the Alpha way!

UPDATE: someone asked in the comments whether incoming calls are announced.

Yes; all incoming calls show up in your taskbar with a popup, and still ring on your phone or any other device you have it set to ring on (with Simulring).

Imagine being able to turn on your notebook in Japan, login to your Vonage account, and have it ring there at the same time as it rings at home, without having to change any settings in your account! Sure, VOIP has always been possible with Vonage, but it was a paid service and was never as well integrated with your regular adapter as this program.

You can find the Vonage Talk application here.