telephonyManager.getCellLocation() gives null

This is my main class

package com.TelephonyManager.home;

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.telephony.TelephonyManager;
import android.telephony.gsm.GsmCellLocation;
import android.widget.TextView;

public class AndroidTelephonyManager extends Activity {

public class OpenCellID {
		  String mcc;  //Mobile Country Code
		  String mnc;  //mobile network code
		  String cellid; //Cell ID
		  String lac;  //Location Area Code
		   
		  Boolean error;
		  String strURLSent;
		  String GetOpenCellID_fullresult;
		   
		  String latitude;
		  String longitude;
		   
		  public Boolean isError(){
		   return error;
		  }
		   
		  public void setMcc(String value){
		   mcc = value;
		  }
		   
		  public void setMnc(String value){
		   mnc = value;
		  }
		   
		  public void setCallID(int value){
		   cellid = String.valueOf(value);
		  }
		   
		  public void setCallLac(int value){
		   lac = String.valueOf(value);
		  }
		   
		  public String getLocation(){
		   return(latitude + " : " + longitude);
		  }
		   
		  public void groupURLSent(){
		   strURLSent =
		    "http://www.opencellid.org/cell/get?mcc=" + mcc
		    +"&mnc=" + mnc
		    +"&cellid=" + cellid
		    +"&lac=" + lac
		    +"&fmt=txt";
		  }
		   
		  public String getstrURLSent(){
		   return strURLSent;
		  }
		   
		  public String getGetOpenCellID_fullresult(){
		   return GetOpenCellID_fullresult;
		  }
		   
		  public void GetOpenCellID() throws Exception {
		   groupURLSent();
		   HttpClient client = new DefaultHttpClient();
		   HttpGet request = new HttpGet(strURLSent);
		   HttpResponse response = client.execute(request);
		   GetOpenCellID_fullresult = EntityUtils.toString(response.getEntity()); 
		   spliteResult();
		  }
		   
		  private void spliteResult(){
		   if(GetOpenCellID_fullresult.equalsIgnoreCase("err")){
		    error = true;
		   }else{
		    error = false;
		    String[] tResult = GetOpenCellID_fullresult.split(",");
		    latitude = tResult[0];
		    longitude = tResult[1];
		   }
		     
		    
		  }
		 }
		 
		 int myLatitude, myLongitude;
		 OpenCellID openCellID;
		 
		  
		   /** Called when the activity is first created. */
		   @Override
		   public void onCreate(Bundle savedInstanceState) {
		       super.onCreate(savedInstanceState);
		       setContentView(R.layout.main);
		       TextView textGsmCellLocation = (TextView)findViewById(R.id.gsmcelllocation);
		       TextView textMCC = (TextView)findViewById(R.id.mcc);
		       TextView textMNC = (TextView)findViewById(R.id.mnc);
		       TextView textCID = (TextView)findViewById(R.id.cid);
		       TextView textLAC = (TextView)findViewById(R.id.lac);
		       TextView textGeo = (TextView)findViewById(R.id.geo);
		       TextView textRemark = (TextView)findViewById(R.id.remark);
		       
		       //retrieve a reference to an instance of TelephonyManager
		       TelephonyManager telephonyManager = (TelephonyManager)getSystemService(Context.TELEPHONY_SERVICE);
		       GsmCellLocation cellLocation = (GsmCellLocation)telephonyManager.getCellLocation();
		       
		       String networkOperator = telephonyManager.getNetworkOperator();
		       String mcc = networkOperator.substring(0, 3);
		       String mnc = networkOperator.substring(3);
		       textMCC.setText("mcc: " + mcc);
		       textMNC.setText("mnc: " + mnc);
		       
		       int cid = cellLocation.getCid();
		       int lac = cellLocation.getLac();
		       textGsmCellLocation.setText(cellLocation.toString());
		       textCID.setText("gsm cell id: " + String.valueOf(cid));
		       textLAC.setText("gsm location area code: " + String.valueOf(lac));
		       
		       openCellID = new OpenCellID();
		       
		       openCellID.setMcc(mcc);
		       openCellID.setMnc(mnc);
		       openCellID.setCallID(cid);
		       openCellID.setCallLac(lac);
		       try {
		   openCellID.GetOpenCellID();
		    
		   if(!openCellID.isError()){
		    textGeo.setText(openCellID.getLocation());
		    textRemark.setText( "\n\n"
		      + "URL sent: \n" + openCellID.getstrURLSent() + "\n\n"
		      + "response: \n" + openCellID.GetOpenCellID_fullresult);
		   }else{
		    textGeo.setText("Error");
		   }
		  } catch (Exception e) {
		   // TODO Auto-generated catch block
		   e.printStackTrace();
		   textGeo.setText("Exception: " + e.toString());
		  }
		   }   
	
}

this is my main xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:orientation="vertical"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   >
<TextView
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:text="@string/hello"
   />
<TextView
   android:id="@+id/gsmcelllocation"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   />
<TextView
   android:id="@+id/mcc"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   />
<TextView
   android:id="@+id/mnc"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   />
<TextView
   android:id="@+id/cid"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   />
<TextView
   android:id="@+id/lac"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   />
<TextView
   android:id="@+id/geo"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   />
<TextView
   android:id="@+id/remark"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   />
</LinearLayout>

this is manifest xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.TelephonyManager.home"
      android:versionCode="1"
      android:versionName="1.0">
    <uses-sdk android:minSdkVersion="8" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"></uses-permission>
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"></uses-permission>
    <uses-permission android:name="android.permission.INTERNET"></uses-permission>
    <uses-permission android:name="android.permission.READ_PHONE_STATE"></uses-permission>

</application>
</manifest>

but when i run this programm it gives me null.
below is exception

when i debug the code telephonyManager.getCellLocation() gives me null.please see attachment.