The new beta vesion of Yahoo! Messenger goes beyond instant messaging to include full-duplex voice over Internet Protocol (VOIP) functionality. This means I can talk to friends in Haiti and Japan on Yahoo! Messenger for free, likely with better audio quality than traditional long-distance service.
While instant message services have provided free VOIP in the past, they have been half-duplex; only one person could talk at a time. Microsoft has offered free voice over the Internet for some time now. My first experience with PC-to-PC voice was in 1996 using Microsoft NetMeeting; NetMeeting was replaced by MSN Messenger in 2000. Yahoo! Messenger version 7 includes voice functions which are half-duplex.
The beta release of the new Yahoo! Messenger allows both parties to speak simultaneously. Granted, older computer sound cards may only allow for half-duplex operations; if your computer is old, it might not be able to record your voice and play your friend's converstaion at the same time. Newer computers should not have to work about this, though.
Oh, this release also includes free "voicemail" features... So you're not online? Your friends can leave you a voice message, much like the delayed instant message delivery feature Yahoo! already supports.
Since the release is beta, you may not want to jump on the bandwagon just yet unless you have a vested interest in doing so, like I do. I'm waiting to see if Gaim will support it right off... my guess is "nope." If Gaim supports it, that would just great! But for my friends around the world... I'll probably be using this pretty soon.