Our SMS gateway has always supported HTTPS but it still allows using HTTP only. As using HTTP only is probably a mistake these days we are going to change our gateway to redirect all HTTP requests to HTTPS next week. We don't expect anything to break as curl, etc., should "just work" but we're posting a PEW just in case anyone has a legacy script they think might need adjusting!
Unfortunately we've had to back out of making this change this week as it caused some unforeseen problems! We'll resolve those problems and make the change again soon.