Here's the code of the HTML page:
<title>HTTPS to SMS</title>
From the documentation for HYPERLINK: "Only certain link types are allowed. http://, https://, mailto:, aim:, ftp://, gopher://, telnet://, and news:// are permitted; others are explicitly forbidden (my emphasis)."
As you can see, sms is not listed so one might reasonably assume that it is explicitly forbidden
Why aim: is included, I don't know, ...