What does "Send SMS" do in Automation?

DESCRIPTION:

The "Send SMS" button indicates a step in an automation where a SMS message should be sent. Automations (a.k.a. drip campaigns) MUST start with a "Send an Email", "Send SMS" (if SMS is enabled), or "Wait for Event" step (Enterprise).

If you do not have SMS enabled for your account, you will see a lock on this button. Contact your Client Success Manager for more information on the SMS program. 

HOW-TO:

As noted, an automation MUST start with Send Email, Send SMS, or Wait for Event. 

The kick-off SMS message can be either a triggered or regular SMS message. This can be created directly in the automation workflow along with any subsequent SMS messages.