Dick Hardt has written a nice overview of Twitter Digits over on Medium:

The email and password prompt popular for the last 20+ years of the web does not work for the emerging markets when their first computer is a mobile phone. The “digital” identifier they have and use to identify themselves to others is likely a phone number, and they are unlikely to have (or don’t know) an email address.

I buy this. It's worth reading the whole article; he does point out, I think rightly, that using phone numbers for many kinds of transactions is problematic.

For me, the most salient point is that everyone on the Internet cannot be guaranteed to have an email address. For those users, a telephone number - the most common digital identifier from the pre-Internet tech world - makes a lot of sense.

It's worth thinking about the things someone without an email address can't do. Not only can't they sign up for a vast array of services, but they also can't participate in the building blocks of the web. In the indieweb community, we often talk about every user having their own domain. I do think that's important, but if you don't have an email address, you can't register a domain name. (This is before we consider the money involved.)

The domain name infrastructure lags behind the user experience of the rest of the Internet by quite some way, but it also lags behind the realities of who is on the Internet, how they're online, and why they're here. If we're going to advocate that everyone has a personal domain, we need to figure out ways for everyone to have a personal domain.

How can we make that first step easier and more accessible? Answering this opens the doors for a more equal web.