Ultrasonic data transfer I am trying to send a short amount of data (10-15 characters) from one mobile device to another via (inaudible) sound within 1-2 seconds. I'd like to be able to deal with normal external noises (chatter, traffic, etc). 

I have a software engineering background, but no experience working with sound or audio. Is there a known/documented solution to address this problem of reasonably reliable ultrasonic data transfer? If you know of a guide or some document that'll explain the concepts to me as I develop out a solution that would be really awesome. 

I've researched a little bit on this topic, but have been unable to find something concrete for ultrasonic communication. Any direction would be much appreciated (and yes, I know I'm a noob here). Thanks.
Even using the highest audio frequencies that a typical mobile device can generate (which are below the ultrasonic range), there is no guarantee that "normal external noise" won't interfere.  Transient impact noises can be quite wide-band.  Therefore one may have to try various forms and levels of redundancy or Forward Error Correction coding (Hamming, Reed-Solomon, etc.), until the reliability probabilities reach a suitable level for your application.  For many (most?) modulation schemes, just lowering the bandwidth sent/used can also improve the reliability probabilities of the channel.