With the latest release of Yahoo Messenger, the cloning is complete. Yahoo Messenger now provides all of the functionality Skype provides. But, the latest avatar of Yahoo Messenger is no match to Skype's audio quality.
Yahoo Messenger has been around for a while and in fact, they introduced voice messaging several years back. But then, the quality has always been spotty.
Then, Skype came along and changed the ball game. Even though Skype was a late entrant, (after AOL, Yahoo, MSN & Google), they virtually raced ahead of everyone to become the leader with unsurpassed audio quality. They also raised the bar by introducing SkypeIn & SkypeOut which is changing the telecommunication landscape across the world.
Not to be left behind, Yahoo played catch up game and introduced PhoneIn & PhoneOut. I am sure AOL, MSN and possibly Google will introduce the same concepts soon if they haven't done already.
I have been Skype & Yahoo Messenger regularly and find Skype's audio quality far better than that of Yahoo from several countries to India. In fact, whenever, I am on the road, I connect to broad band and use SkypeOut to make all my calls totally avoiding expensive hotel telephone charges. (It is another story that broad band charges not cheap either in these hotels.)
But then, most of my contacts are in Yahoo Messenger so, for now I will use Yahoo Messenger for text and Skype for Audio. (I also find the GMail Google Talk handy for its ability to do text messaging with folks who are just logged on to the mail system.)