This is cool. It's a homebrew paging network running on Ham radio frequencies. I believe they have this set up to send DX clusters. That's okay I guess but there's all sort of uses this could be used for. Weather alerts, Skywarn, club reminders, emergency contact, or even getting the attention of someone away from their radio.
I'm not sure if it's related to the above project, but here's one using a modified commercial radio to send the pages: http://oh7lzb.blogspot.com/2010/03/project-pocsag-paging-network.html
Apparently some pagers can be reconfigured to work in the 2m band. The pocsag "modem" can be implemented on an Arduino which is a cheap multiprocessor development board.
I saw some pagers in the flea market at the Hamvention this weekend so the used hardware is definitely available. I don't know what kind of prices they were being sold at. I saw plenty of commercial VHF, UHF and 800mhz radios there also.