using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace AsteriskNotifierCom
{

    [Guid("C9239D8C-68BB-4656-81FC-65AD038AFA04")]
    internal interface IAsteriskNotifierCOM
    {
        [DispId(1)]
        void message(string msg);
    }

    [Guid("65520F46-0CC6-4F4A-BDE2-D0527C0DBDB8"), InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
    public interface IAsteriskNotifierCOMEvents
    {
        void OnOperationCompleted(string message);
    }

    [Guid("202802A2-8E85-4073-9A67-534EDE33D580"), ClassInterface(ClassInterfaceType.None), ComSourceInterfaces(typeof(IAsteriskNotifierCOMEvents))]
    public class AsteriskNotifierCOM : IAsteriskNotifierCOM
    {
        public void message(string msg)
        {
            MessageBox.Show(msg, "Это сообщение COM", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
            for (int i=1;i<10;i++)
            {
                AsteriskNotifierComE Ev=new AsteriskNotifierComE();
                Ev.GenerateEvent(i);
            }
        }
    }
    [ComSourceInterfaces(typeof(IAsteriskNotifierCOMEvents))]
    public class AsteriskNotifierComE 
    {   
      
        [ComVisible(false)]
        public delegate void OperationCompletedDel(string message); //No need to expose this delegate
        public event OperationCompletedDel OnOperationCompleted;   
        public void GenerateEvent(int i)
        {
            this.OnOperationCompleted(i.ToString());
        }
    }

}

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;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            AsteriskNotifierCom.AsteriskNotifierCOM co = new AsteriskNotifierCom.AsteriskNotifierCOM();
            AsteriskNotifierCom.AsteriskNotifierComE ev = new AsteriskNotifierCom.AsteriskNotifierComE();
            ev.OnOperationCompleted += Form1_OnOperationCompleted;
            co.message("привет");
            

        }
        public void Form1_OnOperationCompleted(string msg)
        {
            MessageBox.Show(msg);
        }
    }
}