Hello,
Currently ALM doesn't support the functionality to send a text message from within ( and HP doesn't generally release their roadmap on functionality enhancement plans for the future, so it is uncertain if they will add this in the future or not). ALM can send emails because it uses the smtp conduit to pass the emails along to an smtp server for delivery. The only way I can see this happening would be if you were able to access a web portal to compose and send the text message through and if it were at all possible it would require customized coding added to the work flow. At this time there is no such functionality to perform the task you desire.
Hope this helps.
Dan