I wouldn't be surprised at all if you could do this with previous versions of AIM by simply typing in the user's ICQ number instead of their AIM screen name.

I tried that back when it first became available. It might have been a smarterchild kind of thing, I don't really remember. Either way, my last friend still using ICQ never really forgave me for it, as it attempted redeliver the message every time she signed on. With the logging of deadaim, I've lost the real reason I used to use ICQ (And got tabbed IMs as a bonus).

Matthew