In this article I will explain how to send Free single/bulk SMS through Asp.Net Application.

   There are many websites that allow sending free messages such as Way2sms, FullOnSMS, 160by2, Site2SMS, IndyaRocks.com SMSAbc.com, Ultoo.com, SmsSpark.com SMSFI.com Freesms8, Sms440, BhokaliSMS, etc.

   I will explain it with the help of Site2SMS which uses the online API from Mashape.com.

Getting Started:

Step 1: You have to first register yourself on Site2SMS from where you will get the UserName &
                 Password.

Step2: Now register at Mashape.com, you have to create a sample application at Mashape.com
                for which you will get an API key. For help go to following link,

Step 3: Now as you have the API key, lets create the application, write the following HTML to create the Form:

<table>
<tr>
    <td>
        Your Number:
    </td>
    <td>
        <asp:TextBox ID="txtNumber" runat="server"></asp:TextBox>
    </td>
    <td>
        <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" 

ErrorMessage="Required"
            ControlToValidate="txtNumber" ForeColor="Red"></asp:RequiredFieldValidator>
    </td>
</tr>
<tr>
    <td>
        Password:
    </td>
    <td>
        <asp:TextBox ID="txtPassword" TextMode="Password" runat="server"></asp:TextBox>
    </td>
    <td>
        <asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" 

ErrorMessage="Required"
            ControlToValidate="txtPassword" ForeColor="Red"></asp:RequiredFieldValidator>
    </td>
</tr>
<tr>
    <td>
        Recepient Number:
    </td>
    <td>
        <asp:TextBox ID="txtRecepientNumber" runat="server" Width = "300"></asp:TextBox>
    </td>
    <td>
        <asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" 

ErrorMessage="Required"
            ControlToValidate="txtRecepientNumber" 

ForeColor="Red"></asp:RequiredFieldValidator>
    </td>
</tr>
<tr>
    <td>
        Message:
    </td>
    <td>
        <asp:TextBox ID="txtMessage" runat="server" TextMode="MultiLine"></asp:TextBox>
    </td>
    <td>
        <asp:RequiredFieldValidator ID="RequiredFieldValidator5" runat="server" 

ErrorMessage="Required"
            ControlToValidate="txtMessage" ForeColor="Red"></asp:RequiredFieldValidator>
    </td>
</tr>
<tr>
    <td>
    </td>
    <td>
        <asp:Button ID="btnSend" runat="server" Text="Send" OnClick="btnSend&#95;Click" />
    </td>
    <td>
    </td>
</tr>
</table>

   This Form will take your registered number and password at Site2Sms, Receipent Numbers and the Message to be sent.

Step 4: Now use the Namespace after adding reference of ASPSnippets.SmsAPI.dll, you can download this dll from: `Download Link`
NOTE->This dll contains the definition for the SMS class.

Step 5: Now on click of the send button write the following code:

protected void btnSend_Click(object sender, EventArgs e)
{
    SMS.APIType = SMSGateway.Site2SMS;
    SMS.MashapeKey = "<Mashape API Key>";
    SMS.Username = txtNumber.Text.Trim();
    SMS.Password = txtPassword.Text.Trim();
    if (txtRecepientNumber.Text.Trim().IndexOf(",") == -1)
    {
        //For sending single SMS
        SMS.SendSms(txtRecepientNumber.Text.Trim(), txtMessage.Text.Trim());
    }
    else
    {
        //For sending multiple SMS
        List<string> numbers = txtRecepientNumber.Text.Trim().Split(',').ToList();
        SMS.SendSms(numbers, txtMessage.Text.Trim());
    }
}

Step 6: The SMS is sent.