[jacquesm]

Probably not, but what you could try to do is to transfer data in such a way that people would ignore the sounds because they thought the sounds were not data being transmitted.

Make it sound like birdsong in the presence of other birds, make it sound like fragments of human speech when there are people present, make it sound like fan noise in a DC and so on.

[m0ther]

That is a sexy idea. I feel bad that my second thought was "but likely has no commercial application". Now I wonder when I got old... I'll be writing an audio engine in the next few months; I'll try hacking together something like this then :D.

[jacquesm]

Very cool :) Please let me know if you get it working.

[dddw]

And then you record outside and find out that the birds are gossiping about us humans all along!