SMS Framework - Multiple destination numbers
Assuming your question is about D7, you could try to create a view (using the Views module) of those users that you want to send an SMS to.

After you succeeded in creating such view, you can process the results of a VBO enabled view via Rules, whereas your rule performs 2 Rules Actions (in the rule you already have in place):


Load the VBO list of those users.
Add a loop to perform a Rules Action "send an SMS" (similar to what your current rule already does), for each user contained in your Views results.


For more details, have a look at the tutorial "How to process the results of a VBO enabled view via Rules?".