sentences:  There are three basic functions in a green box, and each one is activated with an MF tone.The green box's designers have noted that it is not possible to use the green box from the payphone being manipulated; it can only be used by the called party.According to the text file "The Green Box" by "The Blue Buccaneer" and "The Tracker", each of these frequencies should be sounded for at least 900 milliseconds.