I am thinking of the endless mobile applications for this. Musicians and their songs, TV and radio ads. It wouldn't have to deliver ads, but something that keeps the consumer connected.
This is another type of physical world hyperlink.
I talked about this concept just a month ago. NTT DoCoMo is the type of company that imagines and then implements innovative mobile technology.
From Unmediated DoCoMo develops sound QR code
NTT DoCoMo yesterday announced that they developed the acoustic OFDM (Orthogonal frequency-division multiplexing) technology, which can be used to embed URLs and text data in broadcast music/audio.
Consumers' mobile phones "listen" to the music/audio and extract the embedded URLs/data. About 100 characters can be transmitted in a second. (To deploy this technology, broadcast stations will need to install a dedicated encoder. Mobile phones need to be enhanced with a decoder mechanism as well.)
DoCoMo thinks this technology can also be used at shopping malls and supermarkets. Then, the sound from in-store speakers would probably be delivering information about specials, ads, discount coupons, etc. ITmedia describes this technology as "Sound QR Code" or "Sound Toruka".
A similar technology exists for ultrasonic sound, however, DoCoMo's technology uses audible sound that can be transmitted through regular speakers.