Yahoo is in the process of integrating Yahoo Messenger with Yahoo Mail and releasing that to users gradually. Some people might see this feature already when they log in to Yahoo Mail beta.
Once you login to Yahoo Mail beta, You can see your status on top. The contact list will show you how many of your contacts are online. When you compose a mail, you’ll have an option to send an email or chat with that contact, if that contact is online. If you choose chat, then whatever you typed in the email already, will be sent as chat.
When you receive a new chat message while you have your email window open, then the chat message will open in a new tab within Yahoo mail. It looks sleek and nice. You can watch the screencast here. Read the Yahoo press release here.
Photo source: Yahoo screencast.
News Source: Downloadsquad.