Base Dialog

public class BaseDialog extends JDialog {

    protected BaseDialog(Frame owner, String title) {
        super(owner, title, true);
    }

    protected boolean dataIsValid() { return true; }

    protected void setModelFromView() {}

    protected JButton stdOKButton() {
        JButton button = new JButton("OK");

        button.setMnemonic('O');
        getRootPane().setDefaultButton(button);
        button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                if (dataIsValid()) {
                    setModelFromView();
                    setVisible(false);
                }
            }
        });
        return button;
    }

    protected JButton stdCancelButton() {
        JButton button = new JButton("Cancel");

        button.setMnemonic('C');
        button.setDefaultCapable(false);
        button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                setVisible(false);
            }
        });
        return button;
    }

    protected void stdLayout(Component widgetBox, 
                             JButton[] buttons) {
        // create button box
        Box buttonBox = Box.createHorizontalBox();

        buttonBox.add(Box.createHorizontalGlue());
        for (int i = 0; i < buttons.length; i++) {
            if (i > 0) {
                buttonBox.add(createHorizontalStrut(5));
            }
            buttonBox.add(buttons[i]);
        }
        matchComponentSize(buttons);

        // create main box
        Box mainBox = Box.createVerticalBox();

        mainBox.add(widgetBox);
        mainBox.add(createVerticalStrut(17));
        mainBox.add(buttonBox);

        // assemble std dialog
        Container cont = getContentPane();

        cont.add(createVerticalStrut(13),  NORTH);
        cont.add(createVerticalStrut(11),  SOUTH);
        cont.add(createHorizontalStrut(11), EAST);
        cont.add(createHorizontalStrut(12), WEST);
        cont.add(mainBox);

        pack();
    }

    protected void matchComponentSize(JComponent[] 
                                                  comps) {
        Dimension size = new Dimension(0, 0);

        for (int i = 0; i < comps.length; i++) {
            if (comps[i].isVisible()) {
                Dimension c = comps[i].getPreferredSize();
                size.width  = (size.width > c.width)? 
                               size.width : c.width;
                size.height = (size.height > c.height)? 
                               size.height : c.height;
            }
        }

        for (int i = 0; i < comps.length; i++) {
            comps[i].setPreferredSize(size);
            comps[i].setMinimumSize(size);
            comps[i].setMaximumSize(size);
        }
    }

    protected Component createHorizontalStrut(int w) {
        return Box.createRigidArea(new Dimension(w, 0));
    }

    protected Component createVerticalStrut(int h) {
        return Box.createRigidArea(new Dimension(0, h));
    }
}

public class MessageDialog extends BaseDialog {

    private JPanel  panel  = new JPanel();
    private boolean cancel = true;

    public MessageDialog(Frame owner) {
        super(owner, "This Space Available");

        createComponents();
        layoutComponents();

        setLocationRelativeTo(owner);
    }

    public boolean canceled() {
        return cancel;
    }

    protected void setModelFromView() {
        cancel = false;
    }

    private void createComponents() {
        panel.add(new JLabel("<html><center><h1>"
                           + "This Space Available<br>"
                           + "Phone 541-601-8583</h1>"));
        panel.setBorder(BorderFactory
                        .createLineBorder(Color.BLACK));
    }

    private void layoutComponents() {
        JButton[] buttons = { stdOKButton(), 
                              stdCancelButton() };

        stdLayout(panel, buttons);
    }
}

Here's how you fire it up!

    private void doMessage() {

        MessageDialog dialog = new MessageDialog(frame);

        dialog.setVisible(true);  // this blocks

        if (!dialog.canceled()) {
            phone("541-601-8583");
        }
    }