Programmatically sending an SMS message from your Windows Mobile is fairly simple these days.

You'll need the WM6 SDK. Start a new Visual Studio 'Smart Device Project', add a reference to Microsoft.Windows.PocketOutlook, then use the following code...

using Microsoft.WindowsMobile.PocketOutlook;

public void Send(string to, string msg)
{
    if ((to != string.Empty) && (msg != string.Empty))
    {
        SmsMessage message = new SmsMessage(to, msg);
        try
        {
            message.Send();
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.ToString());
        }
    }
}

Job done...