July 28, 2012, 7:36 AM — Messages is not just a reskinning of iChat. Sure, the interface looks different. But in addition to its updated interface, Messages introduces a big change to the way instant messaging works on the Mac.
That's because, unlike iChat, it works with the iMessage platform that Apple introduced last year with iOS 5. It still works with standard IM networks such as AIM and Jabber, and it can still send SMS texts to non-iOS phones.
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But iMessage isn't just another messaging platform like those others. Rather, it ties your Mac and iOS devices into a single unified ecosystem. You can--in theory--begin a conversation on your Mac and then pick it up later on your phone. You can--again, in theory--see your entire chat history with a contact, regardless of the devices you used for those chats. And--for better or worse--when someone chats with you via iMessage, you'll be alerted on your Mac as well as on your phone and tablet.
New look and feel
Messages feels different from the moment you open it. Instead of iChat's single column buddy list and separate windows for chats, Messages's default interface has a two-column interface, with contacts on the left and a chatting pane on the right.
Instead of a long list of buddies, that left pane shows you a list of the people you've "conversed" with most recently--name plus the time or date and the last few lines of your previous exchange. You can sort that list chronologically or manually, dragging and dropping people into whatever order you want.
To initiate a conversation, you can either select someone from that recents list or--if the person you want to chat with isn't there--type the person's name or phone number in the To: field at the top of the right-hand pane. You can remove someone from the conversation list by hovering your mouse cursor over his or her entry, then clicking on the little X that then appears.
The right-hand chat area isn't dramatically different from one of iChat's conversation windows: There's a text-entry box at the bottom where you type what you want to say; until you begin typing, it displays the name of the service you're using for a particular chat. At the top, there's a camera button that gives you quick access to video chat--more on that in an bit. And in the main window is a transcript of your previous conversations.