private void btnCompleteTransfer_Click(object sender, EventArgs e)
        {
            SelectCallForm scf = new SelectCallForm(_call.Line);

            if (scf.ShowDialog() == DialogResult.OK)
            {
                TapiCall otherCall = scf.SelectedCall;
                if (otherCall != null && otherCall != _call)
                {
                    _call.CompleteTransfer(otherCall);
                }
            }
        }
        private void btnSwapHold_Click(object sender, EventArgs e)
        {
            SelectCallForm scf = new SelectCallForm(_call.Line);

            if (scf.ShowDialog() == DialogResult.OK)
            {
                var otherCall = scf.SelectedCall;
                if (otherCall != null && otherCall != _call)
                {
                    _call.SwapHold(otherCall);
                }
            }
        }