A Smart Client solution for an enterprise application (e.g., a Customer Relationship Management system) includes a base application (e.g., Microsoft Outlook), and add-in software that interacts with the base application. The add-in software allows the base application to be used to access data and functions of the enterprise application. The add-in software includes an interface manager for accessing items (corresponding to data in the enterprise application) in a data store for the base application, a communications agent in communication (via web services) with the enterprise application, and a synchronization manager in communication with both the interface manager and the communications agent for synchronizing data between the data store for the base application and the enterprise application. In addition to synchronization, Smart Client data can also be converted to and from data for the base application.