private void btnReset_Click(object sender, EventArgs e)
        {
            txbPhoneNumber.Text = "";
            txbLastName.Text    = "";
            txbFirstName.Text   = "";
            txbAddress.Text     = "";
            selectedRowIndex    = -1;

            refreshDataGridView(PhoneAddress.GetAllPhoneAddress());
        }
 private void MainForm_Load(object sender, EventArgs e)
 {
     refreshDataGridView(PhoneAddress.GetAllPhoneAddress());
 }