Use this feature to enable or disable a "welcome" text message sent to a newly subscribed recipient. Default value is "off". Clicking the "Off" button far to the right enables the editor for changes. You can set a different sender number and modify the body of the message.
Far to the right of the screen you have the "Dynamic fields" button, which lists the dynamic fields you can insert into the message text, and allows you to set a default value for each field: for example, the default value for [ first name ] is "Customer": this value will be viewed by recipients if you have enabled the dynamic field but do not have that information.