Use one of your Your Recipient Lists to your SMS broadcast
To see the lists that you have uploaded, click the 
button in the upper right-hand corner of the 
page.
The “My Uploaded Lists” window displays the lists that you have uploaded. To include one or more of your lists in your newly built broadcast, click the open button that is associated with the list(s) of your choosing.
Refer to Creating a New SMS Message for detailed steps in creating an SMS/MMS for your Recipient List.