So are some of the later ones. Twitter built a multi-billion dollar business by duplicating the functionality of email and listserv in a proprietary service.
Listserv had an SMS-oriented design? It automatically made every user their own independent channel that other users could choose to subscribe to?
I don't use Twitter, but saying it's just email/listserv is rather silly. Also, it's only a mutli-billion dollar business by investment; it doesn't generate even 1bn in revenue.
Email-to-SMS gateways have been around a long time. And sure, an email provider could set up a service that automatically gives every email account their own listserv. I'd agree that Twitter's valuation is arguable, but the investor consensus is that it's a multi-billion dollar business, whatever the revenue is.
