hackers that managed to build “blue boxes” — little devices that fooled AT&T’s long-distance switching equipment, and allowed you to make phone calls for free.

Woz read about them in an article which he showed to Steve. They both tried to build one, and to their surprise, it worked! It was Steve who came up with the idea of selling them; he and Woz would go from room to room in Berkeley’s dorms, where Woz was a student, and sell them to interested students. However, this business was illegal and the two of them stopped after they almost got caught by the police.