Abstract: The invention provides, in some aspects, a system for information exchange including groups of portable digital devices that exchange one or more items of data (“first data”) when placed in a range of one another. That exchange is performed by the devices sonically, e.g., using sound waves conducted by air or other medium between the devices—or, if the devices are touching, conducted by plastic or other materials of which they are made. Alternatively, or in addition, the exchange can be conducted optically, via digital data networks, or otherwise.