Yahoo Messenger vs iMessage

Yahoo Messenger
Yahoo! Messenger is an instant messaging client and associated protocol provided by Yahoo!. Yahoo! Messenger offers PC-PC, PC-Phone and Phone-to-PC service, file transfers, webcam hosting, text messaging service, and chat rooms in various categories.
iMessage lets you send messages back and forth with anyone on iPad, iPhone, iPod touch, or a Mac. If you’re a texter, you’ll love Messages on iPhone, iPad, and iPod touch. Now they all come with iMessage, a service that’s an even better kind of texting. Because it’s free for you and anyone texting over Wi-Fi using an iOS device or Mac with iMessage.