When it's time to select a winning phone number from either an SMS autoresponder or an SMS list, there's a couple steps you'll want to take.
SMS Autoresponder
Using a tool like this one, where you can copy and paste all the recipients phone numbers into, and select a winning phone number at random.
SMS List
Using a tool like this one, where you can copy and paste all the subscriber's phone numbers into, and select a winning phone number at random.
* Unfortunately you're unable to use Tatango to message the winner, so this must be done the old fashion way by calling them.