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As the name suggests, Yahoo Instant Messenger is an instant messaging program that lets you send instant messages, pictures and files to other users. Yahoo Instant Messenger also lets you enjoy free PC to PC calls around the world. All you and your friends need is Messenger and a microphone and speakers. If you or your contacts are not online or away from the computer, you can leave a voicemail message. Just like a normal phone you can check your Call History to see all incoming, outgoing and missed calls.

The Contact Cards pop-up when you mouse-over someone's name on your Messenger List. They give contact info and a quick way to connect. Plus you can custom ringtones so you can choose the sound you hear when someone calls your PC. You can even assign special ringtones for different people.

It's hard to find the information, but according to Yahoo, from version 8.1, Yahoo Messenger is supported by Windows Vista.