Metal Gear Solid 3: Snake Eater Easter Egg - The Sorrow's Little Help

At Volgin's torture, after Volgin leaves the room, The Boss will come near Snake and you'll be able to look in first person view. Behind her, you'll see The Sorrow jumping around so he can be seen by Snake, while holding a sign. In it, you can read:
144.75
Now, at the cell, call that frequency on the radio (144.75). Surprise! You'll see "The door has been unlocked" and, when you get out of the radio sceen, the cell door's open.