How to dectect Cube (Trigger) is touched

Could anyone can help me to sort out what I like to do with my iPad? I am very new to Unity and JavaScript.

I have several cubes in my scene, which I am using as a trigger.

I want to show a message box when the cubes were touched. I am able to show a message box when a cube is touched but the message box show all the time without detecting the cube is touched.

Could you anyone show me how to detect the cubes are touched in JS?

Here is my code and I think I have to use Trigger touched function rather than Update() function. but I don't know how to build trigger touched function.

function Update(){

for (var event : Touch in Input.touches){ if (event.phase == TouchPhase.Began){ touchDetect = true; for (var touch : iPhoneTouch in iPhoneInput.touches){ touchPosion = touch.position; } OnGUI(); }//end if if (event.phase == TouchPhase.Ended){ touchDetect = false; OnGUI(); }//end if }//end for }//end Update

function OnGUI () {

 if(touchDetect){
 

GUI.TextArea(Rect(0,0,170,190), "Name: Centre for A\nAddress: Court Raod \nTel: +44 (0)20 1236 92"); GUI.Label(Rect(200,200,100,50), touchPosion.ToString()); }//end if }//end OnGUI

Many thanks in advance.