ISipUserAgent ua;
    public class MyConfigurator : IConfigurationProvider
    {
        string SIP_USER = "";
        string SIP_PASSWORD = "";
        string SIP_DOMAIN = "";
        public MyConfigurator(string user, string password, string domain)
        {
            SIP_USER = user;
            SIP_PASSWORD = password;
            SIP_DOMAIN = domain;
        }
        public void Configure(IConfigurationContext context)
        {
            var registrar = "sip:" + SIP_DOMAIN;
            var accountId = "sip:" + SIP_USER + "@" + SIP_DOMAIN;
            var proxy = "";
            context.RegisterAccounts(new[]
            {
                new AccountConfig()
                {
                    RegUri = registrar,
                    Id = accountId,
                    Credentials = new List<NetworkCredential>() {new NetworkCredential(SIP_USER, SIP_PASSWORD, "*") },
                    Proxy = new List<string>() {proxy}
                },
            });
        }
    }

    public SoftPhone_Widow(string user, string password, string domain)
    {
        InitializeComponent();
        Thread thread = new Thread(Method =>
        {
            ua = Configure.Pjsip4Net().With(new MyConfigurator("user1", "123312", "mangosip.ru")).Build().Start();
            ua.AccountManager.AccountStateChanged += AccountManager_AccountStateChanged;
        });
        thread.Start();
    }

    private void AccountManager_AccountStateChanged(object sender, pjsip4net.Accounts.AccountStateChangedEventArgs e)
    {
        if (e != null)
            MessageBox.Show(e.StatusText);
    }