> why not use that as the unique ID Maybe I don't want to give people my phone number Maybe I have multiple phones Maybe I anticipate changing my phone numbe

> why not use that as the unique ID Maybe I don't want to give people my phone number Maybe I have multiple phones Maybe I anticipate changing my phone number (maybe I hate my current carrier) Maybe I want something easy for people to remember, or catchy "mybusinessname@mybank" Forcing people to use a particular naming regime should only be done if there is a very compelling case for limiting your users