probleam in getting phone time and date !!!

Hi , i want to get phone current time and date . i use this code , but time is not true !!! please help me , where in this code is wrong ???

Code:

---

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

import java.util.*;
import javax.microedition.lcdui.*;
import javax.microedition.midlet.*;

/**
 * @author mahdi
 */
public class Midlet extends MIDlet {

    Display display;
    Form form = new Form("Clock");
    Calendar calendar;


    public void startApp() {

        display = Display.getDisplay(this);
        calendar = Calendar.getInstance();
        calendar.setTimeZone(TimeZone.getTimeZone("GTM"));
        form.append(" Year : " + String.valueOf(calendar.get(Calendar.YEAR )) + "\n" );
        form.append(" Month : " + String.valueOf(calendar.get(Calendar.MONTH)) + "\n");
        form.append(" Day : " + String.valueOf(calendar.get(Calendar.DAY_OF_MONTH)) + "\n");
        form.append(" Hour : " + String.valueOf(calendar.get(Calendar.HOUR_OF_DAY)) + "\n");
        form.append(" Minute : " + String.valueOf(calendar.get(Calendar.MINUTE)) + "\n");
        display.setCurrent(form);

    }

    public void pauseApp() {
    }

    public void destroyApp(boolean unconditional) {
    }
}

---