There is an SMS protocol for HTML anchor links that is supported by most iphones and some android devices, yet due to some automatic handling of links in email content in MMC, we're not able to use it.
See this article which covers how you can use <a href="sms:phonenumber....." so when a user clicks on a link on a supported mobile device, they would have their SMS/text app open for sending a text to that phone number (additionally typically the link would have prepopulated body text as well)
https://stackoverflow.com/questions/6480462/how-to-pre-populate-the-sms-body-text-via-an-html-link
However when we try that in the wysiwig and html content editors, neither work.
As a Marketer who uses both Maropost email and SMS services, I'd love a way to do this and have a contact click an email to open their text message app, prepopulate the text body (say with keyword I've already set up to watch for in my SMS campaigns) and have the proper html pass through into the compilied email, and in the destination inbox.