A network communications system comprises a number of user stations, coupled
via
a data network to a number of service provider host systems. The user stations
are registered as client stations at the host system of a service provider, with
the host system maintaining a database of registered client station identification
data. The host system additionally maintains a directory of the client stations
that are on-line at a given time, determined from periodic messages sent to the
host by each client station. Callers wishing to contact a client station (10) user
first contact the service provider which, from the directory, determines whether
the user is currently on-line. If so, a paging message is generated by the service
provider from data supplied by the caller and sent via the network to the client
station, the address of which is held in the service provider database.
