Want to recieve a msg/read msg using GSM mobile

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO.Ports;
using System.Threading;

namespace WindowsFormsApplication1
{
    public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();
            loadPorts();
        }

        private void Form2_Load(object sender, EventArgs e)
        {

        }

        private void loadPorts()
        {
            string[] ports = SerialPort.GetPortNames();
            foreach (string port in ports)
            {
                cboPorts.Items.Add(port);
            }
        }

    private void cboPorts_SelectedIndexChanged(object sender, EventArgs e)
    {

    }

    private void button1_Click(object sender, EventArgs e)
    {
        SmsClass sm = new SmsClass(cboPorts.Text);
        sm.Opens();
        sm.sendSms(txtPhone.Text, txtMessage.Text);
        sm.Closes();
        MessageBox.Show("Message Sent!");
    }

    private void AddMobNo_Click(object sender, EventArgs e)
    {
        ListBoxNumbers.Items.Add(tbGMobNo.Text);
        tbGMobNo.Text = "";
    }

    private void btnSendGrouped_Click(object sender, EventArgs e)
    {
        SmsClass sm = new SmsClass(cboPorts.Text);
        for (int a = 0; a <= ListBoxNumbers.Items.Count - 1; a++)
        {
            //SmsClass sm = new SmsClass(cboPorts.Text);
            //sm.Opens();
            //sm.sendSms(ListBoxNumbers.Items[a].ToString(), GtxtMessage.Text);
            //sm.Closes();
            //MessageBox.Show("Message Sent Successfully");

            sm.Opens();
            sm.sendSms(ListBoxNumbers.Items[a].ToString(), GtxtMessage.Text);
            sm.Closes();
            Thread.Sleep(10000);
            MessageBox.Show("Message Sent Successfully");

        }
        sm = null;
    }
  }

}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.IO.Ports;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    class SmsClass
    {
        SerialPort serialPort;
        public SmsClass(string comPort)
        {
            this.serialPort = new SerialPort();
            this.serialPort.PortName = comPort;
            this.serialPort.BaudRate = 9600;
            this.serialPort.Parity = Parity.None;
            this.serialPort.DataBits = 8;// Databits are the number of bits in the stream which can be 8 for binary transfer or 7 for text transfer
            this.serialPort.StopBits = StopBits.One;
            this.serialPort.Handshake = Handshake.RequestToSend;// Handshake is a protocol between the sender and receiver for determining the data transfer correctness
            this.serialPort.DtrEnable = true;//Gets or sets a value that enables the Data Terminal Ready
            this.serialPort.RtsEnable = true;//Gets or sets a value indicating whether the Request to Send
            this.serialPort.NewLine = System.Environment.NewLine;
        }
        public bool sendSms(string cellNo, string sms)
        {
            string messages = null;
            messages = sms;
            if (this.serialPort.IsOpen == true)
            {
                try
                {
                    this.serialPort.WriteLine("AT" + (char)(13));
                    Thread.Sleep(4);
                    this.serialPort.WriteLine("AT+CMGF=1" + (char)(13));
                    Thread.Sleep(5);
                    this.serialPort.WriteLine("AT+CMGS=\"" + cellNo + "\"");
                    Thread.Sleep(10);
                    this.serialPort.WriteLine(">" + messages + (char)(26));
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Source);
                }
                return true;
            }
            else
                return false;
        }

        public void Opens()
        {
            if (this.serialPort.IsOpen == false)
            {
                this.serialPort.Open();
            }
        }
        public void Closes()
        {
            if (this.serialPort.IsOpen == true)
            {
                this.serialPort.Close();
            }
        }
    }

}