Sending a document via text/SMS is just as easy as sending via email!
Prepare a document as you normally would, when you get to Add your Participants click on Add Participant. Enter the participant's name and email address (this is still required for delivery of the completed document and notifications). To send via text/SMS click on "+ Add SMS / Text".
Click Next and continue to finish the document. When you click on Send, the signing URL will be sent to the participant(s) via text/SMS using the number you provided.
Note that any automatic reminders will be sent via email, and the final document delivery will be done via email as well.