A messaging system permitting the development and transmission of computer programming from a base station (102) to a mobile communications terminal (MCT) (104) for execution. The user creates programming including conditional logic for transmission to an MCT using a software development workstation (112) at a base station (100). The user programming is designed to extend the functionality of the built-in programming as supplied by the MCT manufacturer. The MCT receives the user programming, and stores it in a memory (204) for later execution, for example, when the manufacturer-supplied operating software initiates execution of the user programming. Messages transmitted from the MCT may be sent during periods of low network activity. The MCT schedules a reasonable number of messages for transmission at a randomly selected time within a certain scheduling window. The scheduling window takes into account network traffic concerns, future messages placed into the queue, and the number of messages present in the queue.