It's hard for me to get too worked up over this.

I mean, do phonebooks still exist? They used to list everyone's numbers and their names and addresses and then leave them on everyone's doorstep. This is just a (partial) phone number and username.

About the worst abuse I can think of is that you have someone's username from another service, and you can maybe find their phone number.

This seems mild compared to, say, Facebook allowing you to search by email and find a user's facebook profile.