Provided is a system and method for providing a converged messaging service, which can be compatibly used with or replace various services, such as an Instant Messaging (IM) service, a Short Message Service (SMS), a Multimedia Message Service (MMS), a Voice over Internet Protocol (VoIP) service, and a PTT over Cellular (PoC) service. To do this, there are defined an architecture and interfacing of a Converged Messaging Client (CMC) and a CM Server (CMS), which are elements of a converged messaging service for being compatibly used with or replacing the various services. In particular, there is suggested a method of enabling interworking between heterogeneous messaging services in an application layer by expending IP Multimedia Core Network (CN) Subsystem (IMS) technology. There is also suggested a method of defining a CM data storage for supporting the converged messaging service and managing a message and metadata stored in the defined CM data storage.