follow these step and you can send sms easily from your own developed portal

This code is woring fine

i had already made use of this.

First visit the website www.smsc11.com and ask for demo

then they will provide username and password for limited use only for  demo

then use this username and password in the api give below in front of uname and pwd

for e.g in API write username in front of uname and password in front of pass

?&uname=dem&pass=dem



sendsms.aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="SMSSEND.aspx.cs" Inherits="SMSSEND" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">



<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Untitled Page</title>
    <style type="text/css">
        .style1
        {
            width: 100%;
        }
        .style2
        {
            width: 502px;
        }
    </style>
</head>
<body>
    <form id="form1" runat="server">
    <table class="style1">
        <tr>
            <td class="style2">
                &nbsp;</td>
            <td>
                <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
            </td>
        </tr>
        <tr>
            <td class="style2">
                &nbsp;</td>
            <td>
                <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
            </td>
        </tr>
        <tr>
            <td class="style2">
                &nbsp;</td>
            <td>
                <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />
            </td>
        </tr>
        <tr>
            <td class="style2">
                &nbsp;</td>
            <td>
                &nbsp;</td>
        </tr>
        <tr>
            <td class="style2">
                &nbsp;</td>
            <td>
                &nbsp;</td>
        </tr>
    </table>
    <div>
   
    </div>
    </form>
</body>
</html>


code required  for this \
sendsms.aspx.cs

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Net;
using System.IO;
public partial class SMSSEND : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string senderusername = "demo";

        string senderpassword = "Demo@567";

        string senderid = "DEMOAC";

      

        string sURL = "www.smsc11.com";

        string num;

        num = TextBox1.Text;

        StreamReader objReader;

        sURL = "http://smsc11.com/corp/extendingsms1.jsp?uname=&pass=&mobile="+ num +"&msg=hi&sender=DEMOAC" + TextBox2.Text;

        WebRequest wrGETURL;

        wrGETURL = WebRequest.Create(sURL);

        try
        {

            Stream objStream;

            objStream = wrGETURL.GetResponse().GetResponseStream();

            objReader = new StreamReader(objStream);
            objReader.Close();
        }

        catch (Exception ex)
        {

            ex.ToString();

        }
    }
}