How to transfer data to a serial port?

I know that in J2ME CommConnection is the connection to use when working with serial port. I know there are the openInputStream and openOutputStream methods , but in fact I don't know how to transfer data from my MIDLet to the COM port ( the USB port into which the phone's cable is inserted , the phone is Alcatel OT-806D ). For example I want to send the text "Hello world". How to achieve that ?

Here are codes :

J2ME :

import java.io.IOException;
import java.io.OutputStream;
import javax.microedition.io.CommConnection;
import javax.microedition.io.Connector;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.midlet.*;

public class SerialPortMidlet extends MIDlet implements CommandListener, Runnable {
    private Command upload = new Command("upload", Command.SCREEN, 0);
    private Command exit = new Command("exit", Command.SCREEN, 1);
    private Form f = new Form("test serial port");
    private Thread uploadThread;
    private CommConnection com;
    private OutputStream os;
    public SerialPortMidlet()
    {
        f.addCommand(upload);
        f.addCommand(exit);
        f.setCommandListener(this);
        uploadThread = new Thread(this);
    }
    public void startApp() {
        Display.getDisplay(this).setCurrent(f);
    }
    public void pauseApp() {
    }
    public void destroyApp(boolean unconditional) {
        notifyDestroyed();
    }
    public void commandAction(Command c, Displayable d) {
        if (c == upload)
        {
            uploadThread.start();
            f.removeCommand(upload);
        }
        else if (c == exit)
        {
            if (uploadThread.isAlive())
            {
                uploadThread.interrupt();
                try {