Download Messages Beta and get a taste of what’s coming in OS X Mountain Lion. When you install Messages, it replaces iChat. But iChat services will continue to work. And Messages brings iMessage to the Mac — just like on iPad, iPhone, and iPod touch running iOS 5. Here are the features you can expect with Messages:
• Send unlimited iMessages to any Mac, iPad, iPhone, or iPod touch.
• Start an iMessage conversation on your Mac and continue it on your iPad, iPhone, or iPod touch.
• Send photos, videos, attachments, contacts, locations, and more.
• Launch a FaceTime video call and bring the conversation face-to-face.
• Messages supports iMessage, AIM, Yahoo!, Google Talk, and Jabber accounts.
More info and download link here.