> What I can't figure out is why did it displace "plain SMS" or other tools. SMS was unreliable, at least back when it was used. It was common for someone to r

> What I can't figure out is why did it displace "plain SMS" or other tools. SMS was unreliable, at least back when it was used. It was common for someone to receive it hours later or at least many minutes later, when it was too late. Informing someone you just got the message they told you about in-person a while back was a common occurrence. You also don't know when a person received your message, so you would opt to call them anyways if they take too long to reply with something even if they were just busy. Basically, the 2 checkmarks on each message is the killer feature. Spam is also a problem with SMS. Email is something that never really took off in mobile devices. I suppose everyone saw it as the same thing as SMS, with the same issues. Perhaps worse, since an email client needed to poll the server for new messages. SMS is something people did since before smartphones. Dumbphones didn't commonly have real support for email. Also, email on a mobile device meant you had to setup the mail client, and you didn't have to setup anything with SMS, just give people your number.