android - telephonyManager.listen forces application to terminate

Iam new with Android, and writting a small application for tracking call events. Every time i try to bind the listner, the os forces the app to close unexspectly. What did i miss? Here is my code:

package com.example.helloandroid;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.telephony.CellLocation;

import android.telephony.PhoneStateListener;
import android.telephony.ServiceState;
import android.telephony.TelephonyManager;
import android.widget.TextView;

public class helloAndroid extends Activity {

TextView textOut;
TelephonyManager telephonyManager;
PhoneStateListener phoneStateListener;

@Override
public void onDestroy(){
telephonyManager.listen(phoneStateListener, PhoneStateListener.LISTEN_NONE);
}

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

 // Get the UI
    textOut = (TextView) findViewById(R.id.textOut);

 // Get the telephony manager
    telephonyManager = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);

    // Create a new PhoneStateListener
    phoneStateListener = new PhoneStateListener() {
     public void onCallForwardingIndicatorChanged(boolean cfi) {}
     public void onCallStateChanged(int state, String incomingNumber) {}

     public void onCellLocationChanged(CellLocation location) {}
     public void onDataActivity(int direction) {}
     public void onDataConnectionStateChanged(int state) {}
     public void onMessageWaitingIndicatorChanged(boolean mwi) {}
     public void onServiceStateChanged(ServiceState serviceState) {

      String stateString = "N/A";
         switch (serviceState.getState()) {
         case TelephonyManager.CALL_STATE_IDLE:
           stateString = "Idle";

           break;
         case TelephonyManager.CALL_STATE_OFFHOOK:
           stateString = "Off Hook";
           break;
         case TelephonyManager.CALL_STATE_RINGING:
           stateString = "Ringing";
           break;
         }
         textOut.append(String.format("\nonCallStateChanged: %s", stateString));


     }
     public void onSignalStrengthChanged(int asu) {}
     };

    // Register the listener with the telephony manager
    telephonyManager.listen(phoneStateListener,
       PhoneStateListener.LISTEN_CALL_FORWARDING_INDICATOR |
       PhoneStateListener.LISTEN_CALL_STATE |
       PhoneStateListener.LISTEN_CELL_LOCATION |
       PhoneStateListener.LISTEN_DATA_ACTIVITY |

       PhoneStateListener.LISTEN_DATA_CONNECTION_STATE |
       PhoneStateListener.LISTEN_MESSAGE_WAITING_INDICATOR |
       PhoneStateListener.LISTEN_SERVICE_STATE |
       PhoneStateListener.LISTEN_SIGNAL_STRENGTH); 

}

}