it's like 2d barcode to check-in facebook places
let's encode url in audio (like encode signature in image)
and play the audio in the mall or restaurant, to let phones auto check-in to facebook place or google places.

can also do auto checkin with wifi wireless router id, or rfid, etc.

usually, 2d barcode are used for input, not for output.
Probably we should make it two ways.

Idea: you scan a barcode, your device connect to an url (OR computer or id) provided in that barcode, then, your device provide your data or upload something.

use 2D barcode to sync two machines (ex: ipad with iphone, xp with android phone, etc)
for presentation, game, remote control, etc.