Emerging high bandwidth wireless infrastructure such as WiFi and Bluetooth networks make possible mobile applications that involve automated "conversations" between mobile devices and other land-based systems. By automated is meant that communication does not necessarily require human initiation or intervention. Such applications have been previously economically unviable on GSM/ GPRS networks due to the costs per call and/ or per data volume and technically challenging as providing for run-time flexibility in such communication poses semantic encoding difficulties. Nevertheless such applications are particularly well suited to mobile device interfaces, which have input and display limitations, as they minimize the required level of human user input. In this paper we propose a two-tier architecture for simple database-centric mobile applications, capable of such automated communication, that uses polymorphism to achieve run-time flexibility.