The IP Multimedia Subsystem (IMS) is a concept for an integrated network of telecommunications carriers that would facilitate the use of IP (Internet Protocol) for packet communications in all known forms over wireless or landline. Examples of such communications include traditional telephony, fax, e-mail, Internet access, Web services, Voice over IP (VoIP), instant messaging (IM), videoconference sessions and video on demand (VoD).
IMS was originally conceived in the late 1990s as part of a plan for worldwide deployment of mobile telecommunications networks that would interface with the public switched telephone network (PSTN). IMS is part of the Third Generation Partnership Project (3GPP).
In its ideal form, IMS would offer unprecedented convenience for individual and business users. Flexibility and expandability would allow vendors to bring new services online as those services emerge and evolve, without forcing subscribers to frequently change carriers. Reality has fallen short of this ideal. It is becoming easier for individuals and businesses to access content outside the control of traditional telecommunications carriers. Small operators may be less willing than large carriers to embrace the IMS paradigm. Some analysts believe that total convergence -- the universal availability of all forms of telecommunications over IP -- may be decades away or may never be realized at all.
IMS also stands for Information Management System and Intelligent Manufacturing Systems.