How to connect an ASP.NET web application to the phone attached to the COM Port?

I am developing a application which can receive SMS messages and after reading it to send replies as SMS. For this, I am attaching a nokia 7210 Supernova via USB to act as the GSM modem for showing demo. This is what in my mind. But I don't know how to proceed with this. Can anyone give me good guidance?? I found a way using AT commands. I just tested using this code snippet: I tried to dial a number. But nothing happened in the phone.

    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;

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button开发者_运维知识库1_Click(object sender, EventArgs e)
        {
            String mobileNumber = "121312";
            SerialPort sp1 = new SerialPort("COM10", 9600);
            sp1.Open();
            sp1.WriteLine("ATD" + mobileNumber + ";");
            sp1.Close();

        }
    }
}

i dont think this is a good idea. there are tons of webservices which are cheaper and faster. the other option if you want 100% control is to connect to a sms gateway of a provider via modem / isdn.