sending sms to many numbers using gsm modem in c#

Question

Hello Guyz, i would like to ask how can i send sms to all number attached here is my source code i can only sent a sms to one phone number but i want to send it to many phone number. thanks  

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.Data.SqlClient;

//============
using System.IO.Ports;
using System.Threading;

namespace StudentInformationSystem
{
    public partial class frmsendingsms : Form
    {
        SqlCommand cmd;
        SqlConnection cn;
        SqlDataAdapter da;
        SqlDataReader dr;
        string _title = "STUDENT INFORMATION SYSTEM";
        public frmsendingsms()
        {
            InitializeComponent();
            academicyear();
        }
        public void academicyear()
        {

            cn = ClassDB.ConnectDB();
            //cn.Open();
            cmd = new SqlCommand("select academicyear from tblAY where status like 'OPEN'", cn);
            cmd.Parameters.AddWithValue("@academicyear", txtacademicyear.Text);
            dr = cmd.ExecuteReader();
            dr.Read();
            if (dr.HasRows)
            {
                txtacademicyear.Text = dr["academicyear"].ToString();
                // txtacademicterm.Text = dr["term"].ToString();
                //cbacademicterm.Text = dr["term"].ToString();
            }
            else
            {

            }

            dr.Close();
            cn.Close();

        }

        private void btnSend_Click(object sender, EventArgs e)
        {
            try
            {
                SerialPort sp = new SerialPort();
                sp.PortName = cbportnumber.Text;
                sp.Open();
                sp.WriteLine("AT" + Environment.NewLine);
                Thread.Sleep(100);

                sp.WriteLine("AT+CMGF=1" + Environment.NewLine);
                Thread.Sleep(100);

                sp.WriteLine("AT+CMGS=\"" + txtPhoneNumber.Text + "\"" + Environment.NewLine);
                Thread.Sleep(100);

                sp.WriteLine(txtMessage.Text + Environment.NewLine);
                Thread.Sleep(100);

                sp.Write(new byte[] { 26 }, 0, 1);
                Thread.Sleep(100);

                var response = sp.ReadExisting();
                if (response.Contains("ERROR"))
                    MessageBox.Show("Send failed!", "Message", MessageBoxButtons.OK, MessageBoxIcon.Information);
                else
                    MessageBox.Show("Message has been sent", "Message", MessageBoxButtons.OK, MessageBoxIcon.Information);
                sp.Close();

            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "Message", MessageBoxButtons.OK, MessageBoxIcon.Information);
            }
        }

        private void txtyear1_TextChanged(object sender, EventArgs e)
        {
            try
            {
                txtyear2.Text = (long.Parse(txtyear1.Text) + 1).ToString();
            }
            catch
            {
                txtyear2.Clear();
            }
            txtacademicyear.Text = txtyear1.Text + "-" + txtyear2.Text;
        }

        private void txtsearch_KeyUp(object sender, KeyEventArgs e)
        {
            cn = ClassDB.ConnectDB();
            listBox1.Visible = true;
            listBox1.Items.Clear();
            SqlCommand cmd = cn.CreateCommand();
            cmd.CommandType = CommandType.Text;
            cmd = new SqlCommand("Select* from tblstudentregistration where lrn like'" + txtsearch.Text + "%' or fullname Like '" + txtsearch.Text + "%'", cn);
            cmd.ExecuteNonQuery();
            DataTable dt = new DataTable();
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            da.Fill(dt);
            foreach (DataRow dr in dt.Rows)
            {
                listBox1.Items.Clear();
                listBox1.Items.Add(dr["lrn"]).ToString();
                //  listBox1.Items.Clear();
                listBox1.Items.Add(dr["fullname"]).ToString();
            }
        }

        private void txtsearch_KeyDown(object sender, KeyEventArgs e)
        {
            try
            {
                cn = ClassDB.ConnectDB();
                if (e.KeyCode == Keys.Down)
                {
                    listBox1.Focus();
                    listBox1.SelectedIndex = 0;
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
        }

        private void listBox1_KeyDown(object sender, KeyEventArgs e)
        {
            cn = ClassDB.ConnectDB();
            if (e.KeyCode == Keys.Down)
            {
                this.listBox1.SelectedIndex = this.listBox1.SelectedIndex;
            }
            if (e.KeyCode == Keys.Up)
            {
                this.listBox1.SelectedIndex = this.listBox1.SelectedIndex;
            }
            if (e.KeyCode == Keys.Enter)
            {
                //search();
                txtsearch.Text = listBox1.SelectedItem.ToString();
                displayresulttextboxs();
                // displayresultontxtboxes();
                listBox1.Visible = false;



            }
        }
        private void displayresulttextboxs()
        {
            cn = ClassDB.ConnectDB();
            // cmd = new SqlCommand("Select * from tblstudentregistration where lrn='" + txtsearchstudentlrn0rFullname.Text + "' and academicyear='" + txtacademicyear.Text + "' and academicterm='" + txtacademicterm.Text + "'", cn);
            cmd = new SqlCommand("Select * from tblstudentregistration where lrn='" + txtsearch.Text + "' and academicyear='"+txtacademicyear.Text+"' and academicterm ='"+cbacademicterm.Text+"'", cn);
            dr = cmd.ExecuteReader();
            if (dr.Read())
            {
                txtsearch.Text = dr[1].ToString();
               txtPhoneNumber.Text= dr[9].ToString();

            }

            else
            {
                cn = ClassDB.ConnectDB();
                // cmd = new SqlCommand("Select * from tblstudentregistration where fullname='" + txtsearchstudentlrn0rFullname.Text + "' and academicyear='" + txtacademicyear.Text + "' and academicterm='" + txtacademicterm.Text + "'", cn);
                cmd = new SqlCommand("Select * from tblstudentregistration where fullname='" + txtsearch.Text + "' and academicyear='" + txtacademicyear.Text + "' and academicterm ='" + cbacademicterm.Text + "'", cn);
                dr = cmd.ExecuteReader();
                if (dr.Read())
                {
                    txtsearch.Text = dr[1].ToString();
                    txtPhoneNumber.Text = dr[9].ToString();


                }
                else
                {
                    MessageBox.Show("There's no Record has been found", _title, MessageBoxButtons.OK, MessageBoxIcon.Stop);
                }
            }
        }

        private void btnsearch_Click(object sender, EventArgs e)
        {

        }
    }
}