Yeah, this was the first messenger service I ever used. Back in the late 90s, it pretty much replaced the telephone for communication among high schoolers. And by the time I was in University, it was more or less ICQ and texting - but texting had limitations back then (like 20 a day, then you pay extra). ICQ was culturally significant until AIM/MSM replaced it, despite the fact that they didn’t seem any better, functionally.
Side note: in Utopia, we used ICQ alongside mIRC to gather people for massive alliance assaults. (gangbangs, as we called them!)
Much like Don, I thought ICQ shut down 15+ years ago.