You can connect any WSS 3.0 or SharePoint 2007/2010 list (no Web part) directly with external data from Microsoft Exchange Server folders, e.g. contacts, tasks, events / appointments, inbox etc.using the
SharePoint Business Data List Connector (BDLC).

You simply can use a connection string and SQL like queries to select your data and provide it in tasks, contacts, events or custom lists with all list features available, e.g. calendar views, calculated fields, RSS newsfeeds, email notifications and workflow, if external Exchange data changes.