PhoneWindow.java

import javax.imageio.ImageIO;
import javax.swing.*;
import javax.swing.event.InternalFrameEvent;
import javax.swing.plaf.basic.BasicInternalFrameUI;
import java.awt.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;

public class PhoneWindow {

    public static void main(String[] args) {
        new PhoneWindow();
    }

    public PhoneWindow() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    final JFrame frame = new JFrame();
                    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                    // create the  inner frame
                    final JInternalFrame frame2 = new JInternalFrame("My Telephone");
                    frame2.setClosable(true);
                    frame2.setDefaultCloseOperation(WindowConstants.DO_NOTHING_ON_CLOSE);
                    frame2.addInternalFrameListener(new javax.swing.event.InternalFrameAdapter() {
                        public void internalFrameClosing(InternalFrameEvent e) {
                            frame.dispose();
                        }
                    });
                    MoveMouseListener mml = new MoveMouseListener(frame);
                    BasicInternalFrameUI ui = (BasicInternalFrameUI) frame2.getUI();
                    ui.getNorthPane().addMouseListener(mml);
                    ui.getNorthPane().addMouseMotionListener(mml);
                    // add elements to the outer frame
                    frame.setUndecorated(true);
                    frame.setBackground(new Color(0, 0, 0, 0));
                    JPanel pane = new TranslucentPane();
                    frame.setContentPane(pane);
                    frame.setLayout(new BorderLayout());
                    // add inner frame and phone picture
                    frame.add(frame2, BorderLayout.CENTER);
                    frame.add(new JLabel(new ImageIcon(ImageIO.read(getClass()
                            .getResource("/transparent-phone.png")))), BorderLayout.EAST);
                    frame.setLocationRelativeTo(null);
                    frame.setMinimumSize(new Dimension(400, 300));
                    frame.pack();
                    // show
                    frame2.setVisible(true);
                    frame.setVisible(true);
                } catch (Throwable ex) {
                    ex.printStackTrace();
                }

            }
        });
    }

    public class TranslucentPane extends JPanel {

        public TranslucentPane() {
            setOpaque(false);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.setComposite(AlphaComposite.SrcOver.derive(0f));
            g2d.setColor(getBackground());
            g2d.fillRect(0, 0, getWidth(), getHeight());
        }

    }

    static class MoveMouseListener implements MouseListener, MouseMotionListener {
        JFrame target;
        Point start_drag;
        Point start_loc;

        public MoveMouseListener(JFrame target) {
            this.target = target;
        }

        public static JFrame getFrame(Container target) {
            if (target instanceof JFrame) {
                return (JFrame) target;
            }
            return getFrame(target.getParent());
        }

        Point getScreenLocation(MouseEvent e) {
            Point cursor = e.getPoint();
            Point target_location = this.target.getLocationOnScreen();
            return new Point((int) (target_location.getX() + cursor.getX()),
                    (int) (target_location.getY() + cursor.getY()));
        }

        public void mousePressed(MouseEvent e) {
            this.start_drag = this.getScreenLocation(e);
            this.start_loc = this.getFrame(this.target).getLocation();
        }

        public void mouseDragged(MouseEvent e) {
            Point current = this.getScreenLocation(e);
            Point offset = new Point((int) current.getX() - (int) start_drag.getX(),
                    (int) current.getY() - (int) start_drag.getY());
            JFrame frame = this.getFrame(target);
            Point new_location = new Point(
                    (int) (this.start_loc.getX() + offset.getX()), (int) (this.start_loc
                    .getY() + offset.getY()));
            frame.setLocation(new_location);
        }

        public void mouseReleased(MouseEvent e) {
        }

        public void mouseClicked(MouseEvent e) {
        }

        public void mouseEntered(MouseEvent e) {
        }

        public void mouseExited(MouseEvent e) {
        }

        public void mouseMoved(MouseEvent e) {
        }
    }

}