Remember ICQ? Back in the late 1990s, it was the chat service that most of us used, with each person identified not by a chosen handle, but by an assigned five-digit number. But after AOL bought the service, a lot of the users went on to other chat clients: AOL’s own AIM, MSN Chat, Skype, Gtalk and many others.

But ICQ is still around and has millions of users, especially outside of the United States (the company itself is Israeli). And now it has also joined several of its peers in adding support for Facebook Chat, which was launched way back in 2008.

In February, we reported that AIM had added Facebook Chat to its supported services, but ICQ actually quietly beat its partner in crime (AOL owns both) to the punch in some sense, having released ICQ 7 back in January with Facebook support. That included a way to do status updates, although Chat has only gone live today.

There’s no need for a guide on how to set it up, like the one we wrote for Pidgin last month; the Facebook Connect login is prominently displayed in ICQ 7, and the Facebook icon is always beside friends who are also on Facebook. Beyond chat, ICQ also allows its users to directly post to friend’s walls and share photos.

In fact, Meebo was far ahead of AIM, ICQ or anyone else when it became  the first chat service to officially add Facebook Chat back in February 2009. But there’s nothing unique about Facebook integration anymore. With the additions we’ve seen early this year, it’s probably fair to say that Facebook is now integrated with most of the world’s major chat services and clients.

And at the rate that Facebook itself is growing, it may be used by the majority of the world’s internet-savvy people before long — excluding China, of course. The real news isn’t that any particular chat service has added Facebook. It’s that Facebook itself is in an enviable position: the social network has the potential to be the core messaging platform that other services revolve around. Not that such dominance has ever lasted long, for anyone.