Mac OS X Mountain Lion is coming this Summer. In the meantime you can download Messages Beta.
Developers have Mountain Lion as of today.
Here’s a link with more details on the Mountain Lion features
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.