An
instant messaging system and a method of
instant messaging between a plurality of clients having IM applications of the same or different types. The IM
system includes a plurality of clients having IM
client applications of the following types: a PC-based
instant messaging client application program (101, 301); a
GSM device (104, 303) forming part of a
GSM network; an internet browser-based
client application 201, 305; and an email-based client application (208, 307). An IM
system host (141, 211, 316) including an IM
server (143, 217, 311) is selectively connected to each of the clients via the direct electronic links or
the internet (117, 213, 309) and provides a prescribed range of functionality to the clients. This functionality includes sending an IM, receiving an IM and identifying which members of a group of clients that a client is a member, or prospective member, of are online. Each client type has a
unique identifier to enable access thereto via
the internet (117, 213, 309) and each client has a single account on the IM host /
server for all of its client types that can access the IM
server (143, 217, 311). The account is identified by a unique identification number (“UIN”) common to all of the client types of that client and each
unique identifier of each client type of a client is matched to the UIN of the particular client.