> Why did Person A (who already had an email address) send a SMS text to Person B (who also already had an email address) to chat?!?
Arguably primarily because they want to chat with them and not email them. The two have vastly different UX beyond just contact discovery.
Before WhatsApp there were ICQ (also number-based!), MSN, Skype... WhatsApp's main contribution over these was indeed using phone numbers and contacts access for automated contact discovery, but I don't think it makes sense at all to characterize it as a usability improvement on email.
Another case in point: iMessage supports email addresses as identifiers too. I don't even have my phone number on there because I consider it a strictly inferior identifier (it changes every time I move countries, I lose it if payments to my operator ever lapse, unlike a TLD I have no way of owning it independently from a phone plan etc.)
>but I don't think it makes sense at all to characterize it as a usability improvement on email.
Chats in general (not WhatsApp specifically) have "better" usability than email for some people because:
+ chats skipp the extra keystrokes of email workflow such as "Compose new email" and then enter an extra "Subject:" line which makes normal people put useless things in there such as "a quick question..." and then put the real conversation in the email body. It's a bunch of extra friction for no reason when communicating informally between friends & family.
+ chat ids such as phone numbers are not given out as freely as email addresses which makes chats have less spam and clutter and more easily isolated to personal communications. Email inboxes are clogged up with a bunch of non-chat mails like shipment notifications from Amazon.
I actually prefer email comms and have told my family to send me emails instead of text chats because I'm always at my desk and can use my full keyboard to type out a reply -- but -- they ignore me and always just send text chats. Normal people have a mental model that's geared toward text chats.
E.g. I saw my aunt again 30 years after she last saw me and one of the first things she asked was "What's your phone #? I want to send you a photo when you were little." And because I received her text, I now have my aunt's phone # in my Contacts app. But I don't have her email address. She never gave it to me; and I never asked for it.
Exchanging phone #s is the natural thing to do between friends & family. On the other hand, exchanging emails is often more natural when interacting in business settings or dealing with people at arms length.
Arguably primarily because they want to chat with them and not email them. The two have vastly different UX beyond just contact discovery.
Before WhatsApp there were ICQ (also number-based!), MSN, Skype... WhatsApp's main contribution over these was indeed using phone numbers and contacts access for automated contact discovery, but I don't think it makes sense at all to characterize it as a usability improvement on email.
Another case in point: iMessage supports email addresses as identifiers too. I don't even have my phone number on there because I consider it a strictly inferior identifier (it changes every time I move countries, I lose it if payments to my operator ever lapse, unlike a TLD I have no way of owning it independently from a phone plan etc.)