This paper describes UMI(Unified Messaging Interface), which is a kind of messaging models and has been widely used in development of mobile value-added service. Then we give a brief description of this model about the overall structure and basic functions, following by an introduction of this model's location in the mobile value-added service development. In order to facilitate discussion, this model is logically divided into four function layers illustrated by the logical structure graph. Then, this paper generally describes the working mechanism and messaging process. On this basis, this paper analyzes the unreasonable structure and inadequate functions of this messaging model. Then we focus on the improvement programs, including the transformation of message buffer (re-organization of buffer), improvement of flow control strategy (such as sliding windows), buffer security reinforcement (overflow alert, alarm, flexible alarm strategy). Finally, we elaborate the significance of this improvement.