Under its skin, Messages is still iChat—an instant-messaging program that connects you to chat partners on several different networks: AOL Instant Messenger (AIM), Yahoo, Jabber, or Google Talk.
Jabber is a chat network whose key virtue is its open-source origins. In other words, it wasn’t masterminded by some corporate media behemoth; it’s an all-volunteer effort, joined by thousands of programmers all over the world. There’s no one Jabber chat program (like AOL Instant Messenger). There are dozens, available for OS X, Windows, Linux, Unix, iPhone, and so on. They can all chat with one another across the Internet in one glorious frenzy of typing.
Behind the scenes, Google Talk uses the Jabber network, so Google Talk doesn’t really count as a different network. But it does mean you can use Messages to converse with all those Google Talkers, too.
Finally, thanks to the Bonjour network-recognition technology, you can communicate with other Macs on your own office network without signing up for anything at all—and without being online. This is a terrific feature when you’re sitting around a conference table, idly chatting with colleagues using your wireless laptop (and the boss thinks you’re taking notes). It’s also handy when you want to type little messages throughout the day to a family member downstairs, or to a roommate 15 feet away.
Your contacts from all of these services are consolidated into a single buddy list.
You log into each network separately ...