A mobile telephone can be configured to interact with external services by using a client application on the telephone that interacts with several external services via an intermediary server. The server sends, to the mobile telephone, configuration information to enable or disable defined sets of functionality in the application, the configuration information depending on and appropriate to the particular external service selected on the mobile telephone and being sent automatically to the mobile telephone over-the-air. An implementation of the invention enables a single client application on the mobile telephone to automatically configure features on/off, and modify the terminology used in resources (such as menus, text strings, bitmap images, sounds, sonic effects etc.) depending on the external system or service that the client is connected to via the intermediary server.