Instagram/Twitter/Github: Informal market which favors the needy, and somewhat the connected.
Phone service: random UID as you suggest, users put aliases in address book. Works great. Plays no favorites, unless you want 555-555-5555.
Internet DNS: restrictions on valid names (to certain TLDs) which are gradually lifted as our name needs increase. Expiration, which favors the needy. Cash market, which favors the rich and needy.
Email: Similar to DNS, but mandatory attachment to domains broadens set of available names. No expiration policy at high demand domains (i.e. gmail).
Phone service: random UID as you suggest, users put aliases in address book. Works great. Plays no favorites, unless you want 555-555-5555.
Internet DNS: restrictions on valid names (to certain TLDs) which are gradually lifted as our name needs increase. Expiration, which favors the needy. Cash market, which favors the rich and needy.
Email: Similar to DNS, but mandatory attachment to domains broadens set of available names. No expiration policy at high demand domains (i.e. gmail).