CDPD
CDPD (Cellular Digital Packet Data) has been around for some time now. It's basically analog cellular data, but uses some reserved pieces of the bandwidth which analog cellular voice doesn't. It definetly has its (low-bandwidth) uses.
In 1997, I realized that what portable computing really needed was wireless data. It was available at the time, but I couldn't quite put together enough pieces to convince myself that I should start paying for such a service.
In early 1999, I decided to start using CDPD. It was available in my area (through Bell Atlantic Mobile), and covered the area that I was going to bike through. I found its coverage adequate, but it certainly didn't live up to its professed 19.2k speed. In practice, I found that dropped packets took a long time to be retransmitted successfully, and because of the encryption layer built into the transport protocol, the data link is completely frozen while waiting for a packet to be retransmitted. Nonetheless, for low-bandwidth communication, it works fairly well; just don't expect to web surf or interactively work on a remote host.
In November of 1999, I cancelled my CDPD subscription in favor of CDMA data. The only feature that I miss is the one-price-pays-for-all-access model, as I paid one fee for unlimited CDPD usage but have to pay by the minute for CDMA.