Notifications for JIRA adds another Workflow Post Function to your workflow designer.
To send an SMS when issues require your attention, edit your workflow, and add the 'Send SMS' post function to your workflow transition.
Select 'Send SMS' from the list of available post functions. 
Fill in the message you want to send (see replacement variables to add issue-based information), and select the destination to whom you want to send the text message. You can choose between: a user defined in the issue (assignee, reporter, custom fields) each user in a group defined in the issue (custom fields) a fixed user each user from a fixed group * a fixed phone number
Press add, and publish your workflow, and you're good to go!