Currently the system only allows http: and https: but it would be great if you could also support the tel: and sms: schemes - thanks
Email templates, theming (headers/footers), maybe other places, but those two were why I voted for it. There are "insert link", but the link types are limited to certain web URLs, not things like your phone for calling or SMS.
Here's how to insert those:
I think it's just a matter of knowing how - we only just added the above support doc.
I see that tel: is an available option, but I'd love to be able to utilize sms: as well!
tel: is really the supported one: https://css-tricks.com/the-current-state-of-telephone-links/
sms: is supported by a few browsers but tel: is supported everywhere, and long tapping on it should give the option to sms instead of call.