It could be most any type of system. My local PD uses a metal-cased laptop computer in each unit running XP, and custom software written by a couple of the local officers along with a relative of one who has a local ISP. Said to be well-encrypted (256 bit key, I think?). This came about after they found that a commercial package the PD bought was essentially worthless. The custom software includes mapping from the city engineer's office of all the streets and intersections (for diagraming accidents), plus electronic versions of all the forms and supplementals for report-writing. All this plus text-messaging, group or all stations messaging, plus in-state DL and veh. registration checks. At the end of the shift, all the officer has to do is pull a floppy out of the drive and he takes all his reports, emails, etc. with them. It's referred to on the air as MDC.
Mark S.