> I'm curious to know if are there restrictions on using license-free
devices/bands for data, provided it doesn't exceed the bandwidth
specifications for voice as it was originally intended. This would be in the
US, FWIW. In other words, could one use a FRS or CB radio as a means of
transmitting periodic telemetry packets (checking of course for a clear
channel before sending)?
>
> JB
The higher the frequency, the quieter the channel (less natural noise).  The
higher the frequency, the more line of sight the path must be.  CB is 27 MHz
+/- and can skip long distances (thousands of miles) very well even at low
power.  So can other peoples signals, so the CB band is rather noisy just
from users.  I would look at higher frequency segments to make signal
recovery easier.  If you get an Amateur licence, then cheap radios, modems
and all sorts of other goodies become available.  Check out www.tapr.org for
some of the data transmission stuff that is going on.  Currently they are
designing a "open source" 900 MHz spread spectrum ethernet radio.  Very
cool.  They also have pic based 1200 baud modems for telemetry transmission.
No code is needed for the licence and the test costs $6.00.
John