A method of establishing a session for interactive message communication between a converged Internet Protocol IP messaging client and one of a Short Messaging SM client, a Multimedia Messaging MMS client, a Push to Talk Over Cellular PoC client and an Instant Messaging IM client in a converged IP messaging service system, the method comprising: transmitting, by the converged IP messaging client to a converged IP messaging server, a Session Initiation Protocol SIP INVITE message for establishing interactive message communication; determining, by the converged IP messaging server, if the SIP INVITE message is received, whether a target client of the interactive message communication supports a converged IP messaging service based on pre-stored subscriber information, and if it is determined that the target client does not support the converged IP messaging service, transmitting the SIP INVITE message to an Inter-Working Function IWF; determining, at the IWF, which has received the SIP INVITE message, a message service type supported by the target client; generating, at the IWF, an interactive message communication request by transforming a format of the SIP INVITE message to a message format supported by the target client and including a response directive, which must be input by a user of the target client in response to the interactive message communication request; transmitting from the IWF the interactive message communication request to one of an SM server, a MMS server, a PoC server and an IM client; and if the IWF receives an acceptance response from the target client in response to the response directive within a response time, the IWF establishes a session for the interactive message communication between the converged IP messaging client and the target client. transmitting, by the converged IP messaging client to a converged IP messaging server, a Session Initiation Protocol SIP INVITE message for establishing interactive message communication; determining, by the converged IP messaging server, if the SIP INVITE message is received, whether a target client of the interactive message communication supports a converged IP messaging service based on pre-stored subscriber information, and if it is determined that the target client does not support the converged IP messaging service, transmitting the SIP INVITE message to an Inter-Working Function IWF; determining, at the IWF, which has received the SIP INVITE message, a message service type supported by the target client; generating, at the IWF, an interactive message communication request by transforming a format of the SIP INVITE message to a message format supported by the target client and including a response directive, which must be input by a user of the target client in response to the interactive message communication request; transmitting from the IWF the interactive message communication request to one of an SM server, a MMS server, a PoC server and an IM client; and if the IWF receives an acceptance response from the target client in response to the response directive within a response time, the IWF establishes a session for the interactive message communication between the converged IP messaging client and the target client.