In this post Send Festival Wishes SMS to all registered Students

Important Namespaces Used
--------------------------

using System.IO;
using System.Net;
using System.Collections.Specialized;
using System.Data;
using System.Data.SqlClient;

--------------------------

Retrieve Data Button Click Event Coding
----------------------------------------

 GridView1.Visible = true;

----------------------------------------

Send Button Click Event Coding
----------------------------------------

string sname;
        string mobileno;
        String mycon = "Data Source=sk-pc; Initial Catalog=RegisteredStudents; Integrated Security=True";
        String myquery = "Select * from studentdata";
        SqlConnection con = new SqlConnection(mycon);
        SqlCommand cmd = new SqlCommand();
        cmd.CommandText = myquery;
        cmd.Connection = con;
       SqlDataAdapter da = new SqlDataAdapter();
       da.SelectCommand = cmd;
        DataSet ds = new DataSet();
        da.Fill(ds);
        int nrow;
        nrow = ds.Tables[0].Rows.Count;
        int i = 0;
        while (i < nrow)
        {
            sname = ds.Tables[0].Rows[i]["sname"].ToString();
            mobileno = ds.Tables[0].Rows[i]["mobileno"].ToString();
            sendsms(mobileno, sname);
            ListBox1.Items.Add(mobileno + " " + sname);

            i = i + 1;
        }
        Label3.Text = "SMS Sent Successfully to All Students";
        con.Close();
        GridView1.Visible = false;
        ListBox1.Visible = true;

------------------------------------------

private void sendsms(string mnumber, string sname)
    {
        string destinationaddr =mnumber;
        string message = TextBox1.Text;
        string result;
        String message1 = HttpUtility.UrlEncode(message);
        using (var wb = new WebClient())
        {
            byte[] response = wb.UploadValues("https://api.textlocal.in/send/", new NameValueCollection()
                {
                {"apikey" , "USE YOUR API KEY HERE"},
                {"numbers" , destinationaddr},
                {"message" , message1},
                {"sender" , "TXTLCL"}
                });
            result = System.Text.Encoding.UTF8.GetString(response);



        }