You could put a lot of effort into adding stuff on top to make it more secure, for example public key authentication and encryption. But maybe it's time for SMS

You could put a lot of effort into adding stuff on top to make it more secure, for example public key authentication and encryption. But maybe it's time for SMS to go away. It's very limited compared to other communication methods, and there's only so much you can bolt on afterwards. And there are plenty of alternatives...