Designed by Janis Pönisch, Sören Grünert, and Kirsten Hüsig, "Call a Ball" is a new concept in the form of a soccer ball vending machine -- users have to send an SMS to authorize the dispensing of a ball. Thanks to an RFID-chip embedded into each ball, the machine knows its location at all times. Video demonstration after the jump.
If you want to find people with whom to play ball, all you have to do is register as a 'baseplayer' at one or more kiosks. Then send out an SMS containing the codeword 'Challenge' to the kiosks of your choice, which will then relay it to your teammates and opponents.