The days when the acronym "CDPD" appeared in multiple Network World articles each week (I was the beat reporter then) seem like ancient history. Actually, it was circa 1994 and 1995.The hot mobile networks for public safety, transportation and field service organizations then were the RAM Mobile Data and IBM\/Motorola ARDIS networks, which ran at 4K to 8K bit\/sec.\u00a0 So news of Cellular Digital Packet Data deployments, with blazing maximum rates of 19.2K bits\/sec, and roaming agreements among the CDPD network operators was a big deal.Still, it was always envisioned that IP-based CDPD, initially championed by McCaw Cellular (which morphed into AT&T Wireless), would be usurped by Code Division Multiple Access (CDMA)-based technology. It's time for the CDPD transitions to begin, if they haven't already.The Federal Communications Commission decided a while ago to allow the mobile operators to discontinue CDPD services.\u00a0 AT&T Wireless stopped selling the service early this year and will reportedly discontinue supporting it in June 2004.But there are a couple of thorny issues with getting CDPD customers to move to today's 2.5G and 3G networks.\u00a0 One is that IP addresses used by mobile applications to authenticate users, redirect service requests and so forth were programmed into CDPD modems. But in 2.5\/3G networks, IP addresses are assigned dynamically. So users of CDPD services and devices either have to rewrite their applications or find another solution.The distaste associated with rewriting applications has caused at least two mobile operators - AT&T Wireless and Sprint PCS - to call upon NetMotion Wireless to supply, basically, a middleware migration strategy.NetMotion's Mobility software, among other things, shields applications from the underlying network protocol, allowing the use of IP apps over any wired or wireless network. Meanwhile, users can roam among different kinds of networks - wireless LANs to mobile WANs, for example - as long as they are running IP. Their sessions will quietly be handed off with no disruptions, even if they are out of coverage for a while.Sprint is trying to woo both its own and other carriers' CDPD customers to its CDMA-based network by giving away a CDMA card and NetMotion Wireless software if you sign on for its PCS Data Connect service, which tunnels mobile users to the corporate network over a secure IP VPN or frame relay virtual circuit.Want to start an office pool as to when Verizon will hop on the NetMotion Wireless bandwagon for its CDPD users?