StartTween.cs

using UnityEngine;
using System;
using Random = UnityEngine.Random;
using System.Collections;

public class StartTween : MonoBehaviour {
	
	public GameObject target;
	
	void OnGUI() {
		if (GUI.Button(new Rect(0,0,100,10), new GUIContent("Ok"))) {
			Hashtable args = iTween.Hash(
				"volume", 0,
				"onComplete", "MessageMe"
			);
			iTween.AudioTo(target, args);
		}
	}
	
}

Test.cs

using UnityEngine;
using System;
using Random = UnityEngine.Random;
using System.Collections;

public class Test : MonoBehaviour {

	void MessageMe () {
		Debug.Log("I was messaged");	
	}
	
}