POCSAG is an asynchronous protocol used to transmit data to pagers. The name is an acronym of the Post Office Code Standardisation Advisory Group, the name of the group that developed the code under the chairmanship of the British Post Office that used to operate most telecommunications in Britain before privatization. Before the development and adoption of the POCSAG code, pagers used one of several proprietary codes such as GOLAY, (Binary Golay code).
In the 1990s new paging codes were developed that offered higher data transmission rates and other advanced features such as European and Network roaming. The POCSAG code is generally transmitted at one of three data rates; 512, 1200 or 2400 bits per second.
With Super-POCSAG 1200 bits per second, or 2400 bits per second transmission rates are possible. Super-POCSAG has mostly displaced the POCSAG in the developed world but the transition is still in progress.

and then there was … DAPNET

The DAPNET (Decentralized Amateur Paging Network) is a network operated by amateur radio enthusiasts. It is the new and further developed version of the FunkrufMaster. It consists of a decentral server cluster feeding paging data to distributed transmitters. The most used frequency is 439.9875 MHz and the protocol is POCSAG. Common paging receivers are of type Skyper or AlphaPoc, but there exist others as well. As it is used on amateur radio frequencies, commercial use is forbidden.
Dapnet Wiki

Happy Paging 🙂