[edits Jan. 31] A poli sci friend recently blogged about the Ukranian government’s “text that changed the world,” a mass text message thousands of anti-government demonstrators in Kiev. She asked 1) How did the government know who was in the main square of Kiev that day? (Cell phone location) and 2) How did it send the same message to everyone at once? (Mass SMS)
The second question is easy: phone companies routinely provide mass-SMS services to large customers. For example, I’m on the “emergency alert” texting service of UC San Diego’s campus police. It was designed for earthquakes, but it has been used for other kinds of messages “between earthquakes.” The same message goes out to every phone number on their list.
What to do to avoid tracking? Short version: Leave your phone at home. Second best is to shut it off or switch to airplane mode, but those work only if the government is not making an effort to target you.