Beginning Monday, some Yahoo Mail users will be able to chat in real
time through their e-mail program. Yahoo said in November that it would
embed instant-messaging technology directly into its Yahoo Mail program
so that users wouldn't have to open up--or even install--Yahoo
Messenger or another IM ,service to chat with each other online.
The rollout is set to be phased over several months.
Google added chat to Gmail a year ago, but the experience is not as integrated as the new Yahoo Mail chat functionality, Yahoo has said.
AOL's AIM Triton offers integrated e-mail, instant messaging, SMS text messaging, and voice and video chat.
Refer the pic below:
http://i.n.com.com/i/ne/p/2007/ymailmessenger_550x382.jpg