Finally…
Messages, as it’s called in Mountain Lion, will replace iChat, the chat software Apple includes out of the box. Users will still get access to IM networks like AIM, Yahoo, and Jabber, though Apple’s added compatibility with the same iMessage service that was introduced as part of iOS 5, which Apple says has now served up 26 billion messages since its October launch. Messages can be used to send and receive iMessages with these users for free, and the conversation can be picked up and continued from any device with that same Apple ID and iMessage enabled.
Read more: http://news.cnet.com/8301-27076_3-57378751-248/apple-mac-os-x-mountain-lion-takes-more-bites-out-of-ios/#ixzz1mYeeRyJC

