Don't forget that if there is a built-in mobile phone app that can respond to a "sonic swatch" (great name!) then it could monitor the phone conversation and quietly add it to it's address book.
"Thank you for your order, sir. How would you like to pay?"
"With bitcoins, please."
"No problem, sir. Since we're on the phone do you support sonic swatches, and is it active?"
"Yes, and hold on while I switch it on.... done."
"Thank you. Sending now, it will have an address starting with 12qk for 3.25 BTC."
"The swatch has been sent, sir."
"Hold on... Looks OK... sending... and done."
"Thank you, sir. I can see an unconfirmed transaction against that address. Once it has fully confirmed we will send you an email to confirm the despatch details. Is there anything else I can help you with today?"
Imagine if you could have that conversation with your local railway station car park management company. Once they've sent you their address, you don't need to phone them again. It's unique between you and them so can be tied into their number plate recognitiion system.
There are loads of opportunities for a system like this. Good work, Jim!
I just want to draw your attention to the fact that this is in principle very similar to the data transimission used for fax copiers.
And now look how widespread this technology still is in the industry and private business despite much the internet and much faster data transmission technologies!
Personally I think that the use case pointed out by Gary will be the most used.
If I can get the codec reliable enough, I am tempted to add it into MultiBit as another way of transfering bitcoin URIs in and out in addition to the existing QR codes/ swatches. At under 2 seconds to transfer it I think it is acceptable and I think Java sound is supported on all of Mac/ Win/ Linux (I will have to look into that).
It is such a nice combination of low tech and high tech.
Jim, I want to encourage you to implement it in MultiBit and see if it gains followers.