It is not a joke. John Savio made a special Halloween Costume using a real 40 inch LED panel attached with his iPhone 4. To connect the two devices he used VGA Out app available in Cydia Store for jailbreaked iPhone 4.
He uses a mini 12v Battery with 2+ hours of battery life for the LED panel. The costume took a total of 3 days / 40 hours to complete. See the pictures and watch the video after the break.
And here is the video:
