Facebook news available from Facebook blog to read on their announcements. From the blog it says that Video calling will be available next week but if you visit http://www.facebook.com/videocalling, you can see that it's already availble.
Here's an excerpt from Facebook news blog.
Over the last year, the messages team has been working to make it easier to have one on one conversations with your friends. In November, we launched the new messages, which brings together your chats, texts, emails and messages all in one place.
Today I'm excited to introduce video calling and other improvements to chat.
See The Friends You Message Most
The new chat design includes a sidebar that lists the people you message most. Now it's easier to find your friends and start a conversation. The sidebar adjusts with the size of your browser window, and it automatically appears when the window is wide enough.
Create a Group Chat Instantly
We're also launching multi-person chat, which is one of our most requested features. Now when your friends can't figure out what movie to see, you can just add them to a chat and decide together. To include more friends in your conversation, simply select Add Friends to Chat.
And just like your other chats, the history of your conversation is available in messages.
Bring Your Conversations to Life
Video chat has been around for years now, but it's still not an everyday activity for most people. Sometimes it's too difficult to set up, or the friends you want to talk to are on different services.
Read more here.