Android :: TelephonyManager.listen Forces Application To Terminate

I am 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("
onCallStateChanged: %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);