Abstract-Following the success of short messaging service (SMS), multimedia messaging service (MMS) is emerging as a natural but revolutionary successor to short messaging. MMS allows personalized multimedia messages containing content such as images, audio, text and video to be created and transferred between MMS-capable phones and other devices. By using IP and its associated protocols, MMS is able to interwork with other messaging systems such as Internet messaging services. An important feature of MMS is the guaranteed delivery of messages via a store-and-forward mechanism which temporarily stores messages in the network until successfully delivered. Unlike SMS, multimedia messaging service does not mandate any maximum size for a multimedia message. This enhanced flexibility of MMS requires a careful design of the network in order to avoid excessive message delays and losses. This paper develops a mathematical model for evaluating the performance of an MMS system. Using the model, closed-form expressions for major performance parameters such as message loss, message delay and expiry probability have been derived. Furthermore, a simple algorithm is presented to find the optimal temporary storage size for a given set of system parameters. The accuracy of the presented analysis is evaluated through simulations which shows a close agreement between analytic and simulation results.