Now that FaceTime has been released for the Mac, you can video chat with friends to and from your desktop or laptop as well as your iPhone. If you regularly chat with someone, Mac OS X Hints reader jcrossley has a way to create desktop shortcuts that will call that person on FaceTime:
In Safari's address bar, type in one of the following URLs:
phone# are the Apple ID, e-mail address, or phone number of the person you want to call, respectively. Now select that URL in the address bar and drag it to the desktop, That will create a desktop shortcut that, when double clicked, will open up FaceTime with your friend's information already entered. Just hit the big green button to call them.
You can also use this trick to add one of these Facetime links to Address Book. Just open up Address Book, go to Card > Add Field in the menu bar, and hit URL. Paste the FaceTime link into the URL section, and save the contact. Now, to FaceTime with that person, you can just navigate to their Address Book card and hit the link under the URL entry.