Note : The following post is quite old and google has removed reference links provided.
What it is
A Google Talk chatback badge allows others to chat with you even if they haven’t signed up for Google Talk on their Google Account or if they don’t have a Google Account. You can put the badge in your blog or website, and people who visit those pages can chat with you. The badge will display your online status (whether you’re available to chat or not) and, optionally, your status message.
What I need in order to create one
You need to be a Google Talk user to create a badge, and you’ll need to be online and available (with a green ball next to your name) in Google Talk to enable people to chat with you. If you’re not a current Google Talk user, you’ll need to create a new Google Account. If you have Gmail on your Google Account, you can use Google Talk with your Gmail username and password. You can also use the Google Talk Gadget; just go to http://www.google.com/talk/ and click ‘Launch Google Talk Gadget.’
Let’s create one!
- To create your chatback badge, visit http://www.google.com/talk/service/badge/New. If you’re using a Google Apps account, you can create a chatback badge by visitinghttp://www.google.com/talk/service/a/DOMAIN/badge/New where DOMAIN is the name of your domain.
- From the page, copy and paste the HTML into the source of your webpage where you want the badge to be displayed. You’ll know it’s working if you see a large Google Talk bubble showing your current online status along with the message ‘Chat with [your name]‘ (or whatever you selected as your badge title).
To see this application in a live website visit : Datta Global Traders. This is a site which i have created and implemented this feature. Its wasy and fun..