When sign into my yahoo mail you might get the following message “You can chat with friends on Windows Live™ Messenger right from your Yahoo! Mail. Click Add Contacts to scan your addresses and invite these friends to chat”.
Basically this feature allows you to Instant message friends on Other Networks friends who use Windows Live™ Messenger, Reuters Messaging, and Lotus Sametime — right from Yahoo! Messenger.
Once you click add contact button you will see Windows Live Contacts list. Check the contacts who you want to chat.
Note: Windows Live Contacts must approve your request before you can chat with them.
How to get rid of this message
If you want to get rid of this message, you have to disable the chat feature of Yahoo Mail, ie sign out of your yahoo mail chat.
For Yahoo! Classic Mail:
On the left pane just change your status to Sign out of chat which will make your yahoo mail chat go offline.
All-New Yahoo! Mail:
On the Yahoo! Mail chat status menu, change your status to Sign out of chat.