Yahoo! Messenger beta 3 for the Mac adds voice calling
With the latest version of Messenger for the Mac, users can make free PC-to-PC calls (yes, a Mac is a PC too) to other Messenger buddies. You can also sign up for a Phone Out account to make calls to landlines and mobile phones. Or, if you want to go all the way, you can sign up for a Phone In account, which assigns you a number so people can call you on your PC.
In other words: picture Skype, but with a big yellow smiley face instead of a cool blue talk bubble.
Check out the Yahoo! Messenger blog for a complete rundown of the new features and a handy screencast.