private void btnTransfer_Click(object sender, RoutedEventArgs e)
        {
            if (Model.SelectedCall == null)
            {
                return;
            }

            if (!Model.SelectedCall.CallState.IsInCall())
            {
                return;
            }

            TransferModel  transferSettings = new TransferModel(Model.PhoneCalls, Model.SelectedCall);
            TransferWindow tranferWin       = new TransferWindow(this, transferSettings);
            bool?          ok = tranferWin.ShowDialog();

            if (ok != null && ok == true)
            {
                // blind transfer
                if (transferSettings.TransferMode == TransferMode.Blind)
                {
                    Model.BlindTransfer(transferSettings.BlindTransferTarget);
                    return;
                }

                // attended transfer
                if (transferSettings.TransferMode == TransferMode.Attended)
                {
                    Model.AttendedTransfer(transferSettings.AttendedTransferTarget);
                    return;
                }
            }
        }
        private void btnTransfer_Click(object sender, RoutedEventArgs e)
        {
            if (Model.SelectedCall == null)
                return;

            if (!Model.SelectedCall.CallState.IsInCall())
                return;

            TransferModel transferSettings = new TransferModel(Model.PhoneCalls, Model.SelectedCall);
            TransferWindow tranferWin = new TransferWindow(this, transferSettings);
            bool? ok = tranferWin.ShowDialog();
            if (ok != null && ok == true)
            {
                // blind transfer
                if (transferSettings.TransferMode == TransferMode.Blind)
                {
                    Model.BlindTransfer(transferSettings.BlindTransferTarget);
                    return;
                }

                // attended transfer
                if (transferSettings.TransferMode == TransferMode.Attended)
                {
                    Model.AttendedTransfer(transferSettings.AttendedTransferTarget);
                    return;
                }
            }
        }