I always liked ICQ, but there was always a tad bit of friction remembering huge strings of numbers as practical IDs, and the naming schemes came way later.
11984431 or whatever doesn't roll off the tongue very well.
But Mail.ru deleted old accounts. So...
They even tell you that you can't restore in anymore.
So I know my first library card number was 1000102772901. I had to replace the card a few times, getting new numbers, but I only ever remembered the first one.
On the topic of New ICQ, it looks like all those other multi-user messengers. I wish everyone would switch to Jabber were there are clients for people who don’t have group messaging as their primary use case.