I used ICQ. To tell you when, my UIN was 3393702. >.> Low 7 digits!

I was actually laughing about this earlier today about Newgrounds, which has the same list.

I didn't use Trillian in specific, but I used Pidgin and Adium. Even today I use a program of my own creation to log into multiple services at once, although those services are shutting down one by one.