To send automated SMS when a Lead is created, all you need to do is configure a workflow rule on the Lead object with the below configurations:

  1. Go to "SMS on workflow" addon from the app drop-down on the top-right corner in your org and create a new XML.
  2. Choose all the necessary details for the SMS to be sent out when the workflow rule is triggered

  3.  Choose the recipient type. If you wish to send SMS to the Lead, choose "Mobile phone field" and choose the field containing the contact number in the "Available Recipients" section
  4. Choose the value for the Name field, sender ID and the Template.
  5. Click on "Create". A new XML would be created for this which you need to copy.
  6. Create a workflow rule on Lead and set the Evaluation Criteria as "whenever the record is created"

Paste this XML configuration in the comment section of the task associated with the Workflow rule and activate it.