Not a message, but a date. There's this huge national exam called ENEM that is like SAT that every Brazilian in age to enter a college takes. Millions of students are taking it every year at the same date and time, as its result is what determines who enters in the best universities. Obviously, security against cheating is a huge concern and so everyone must have their phones turned off and sealed in a bag that stays in front of the class until they finish the exam. Now I can only imagine the chaos that would be if an alert was sent in that day.