CompuServe accounts, which were all numbers? Mine was 72125,1424. Or ICQ, which was fun to guess just when the other person signed up by the numeric value of their ICQ account. I'm glad to see ICQ is still operating, which maybe I should have noticed before. I wonder if my old number still works?
Now people use names for their email, in a standard and well understood form that works seamlessly between different service providers. Me@example.com is far more understandable than 72125,1424 ever was.