Back in the late 80s through the 90's, two-tone paging was pretty popular. Many repeater controllers were setup to send these. Hams caring around the popular Minitor pagers on their belts could be summoned via a touch-tone invoked setup on the repeater. You don't see much of that anymore for whatever reason. The only people you noticed still being voice paged are usually volunteer fire / EMS guys.
The idea of digital paging always interested me, but it never seem to have gotten much attention in the ham radio world. Perhaps now that digital voice formats are emerging it's time to touch briefly on the idea again.
Back in the 90's Clive Cooper, G8UNK wrote a software POCSAG digital paging encoder. Kantronic's also came out with the KPC-9612 TNC cable of encoding POCSAG. (If you are wondering what POCSAG is, it's a well known standard for radiopaging)
Paging is kind of a one way deal, much like those beaconing the APRS locations. If this sounds interesting, here is a link for more information:
http://www.qsl.net/kb9mwr/projects/pager/plan.html
