The idea behind allocating frequencies for amateur use is that hams could engage in a hobby with no commercial use which provides an infrastructure for emergency public service communications. To prevent any commercial use of those frequencies, to facilitate enforcement of the rules, and to facilitate the participation by anyone who obtains the proper knowledge and equipment, it is illegal to transmit in a way that "obscures the meaning" of the transmission to people who would want to listen in. So, for example, morse code and ASCII are the only exceptable digital codes, and various modulation techniques are standardized as the technologies are developed. In any case, the amateur frequencies are specifically reserved for non-private communications and are subject to restrictions that have nothing to do with the terms under which other commercial frequencies are licensed. Those frequencies may be licensed for uses that include private communications of some sort. And, since the regulations are based on the principal that broadcast spectrum is a fixed, limited resource, none of this applies to communications carriers who do not operate by broadcasting over the air. -- sidney <sidney@apple.com>