Yahoo Messenger is a free service that allows you to see when friends come online and to send them instant messages.
-Instant Messaging: Send text messages in real-time to your friends on Yahoo! Messenger.
-Chat Rooms: Join a chat room to meet new friends while you discuss your favorite topics.
-Photo Sharing: Share photos from your desktop or Flickr, then discuss them over IM while you and a friend view them together.
-PC-to-PC Calls: Make a voice call to another Yahoo! Messenger user for free (microphone and speakers/headset required).
-Phone Out (PC-to-Phone Calls): Call friends on their regular or mobile phones from Messenger for as low as 1¢ a minute (Phone Out account required).
-Phone In (Get a Phone Number for Messenger): Get a new phone number that allows you to receive calls in Yahoo! Messenger (Phone In account required).
-SMS (Text Messaging): Send text messages from Messenger to your friends mobile phones for free.
-Webcam: Plug in your webcam to share live video with your friends on Yahoo! Messenger.
-IM Conferencing: Instant message with many friends at once in a conference room (includes voice capabilities, where available).
-IM with Friends on Other Networks: IM with friends who use Windows Live Messenger, Reuters Messaging, and Lotus Sametime — right from Yahoo! Messenger.
-File Transfer: Send files instantly to a friend while you IM (2 GB limit).