As indicated above, pagers still exist in medicine and tech support.

I'm currently doing a little consulting work for a medical center, and in the meetings I attend all of the lower-level medical directors (RN's) carry pagers. Don't know if they work outside the campus, though.

Worked for a state agency a couple years ago and their "key" IT people had pagers linked to their mainframe. In addition to the normal person-initiated paging, the mainframe had some monitoring software that could page them if it detected a problem.

Fire and police departments ues 'em, too. Especially volunteer FD's.