CDPD is "Cellular Digital Packet Data."  The last time I paid attention, the
idea was to be able to utilize the "idle" "callspace" (necessary to ensure a
given response time in a cellular network) to send "cheap" packetized data.
The scheme was complex and full of then-current ideas of appropriate network
standards, and seemed to me to be doomed to chronic insufficient bandwidth
to do anything useful (and that was before the Internet's recent explosive
growth.)  I vaguely recall hearing that they've updated to more current
standards buzzwords (ie "ATM" replaces "TP4", or somesuch) and somewhat
higher bandwidth (but probably not high enough!)

Is it actually available ANYWHERE?  Can someone summarize it from a modern
user perspective?

Meanwhile, cellular rate structures have changed, and so have usage patterns
and importance of The Internet.  Lacking common availability and REALLY good
cost incentives, I would bet good money that you'd get a better solution
using off-the-shelf cell phones and cellphone modems.

BillW