Most people at Defcon use a "burner phone" (a cheap supermarket feature-phone) while there. Nobody who is sane would turn on their work phone anywhere near the Defcon conference. I go there every year with a throwaway phone and laptop.
So nobody will see a text message in a timely manner, unless they knew the burner phone number.
So nobody will see a text message in a timely manner, unless they knew the burner phone number.