You can download the document "How to develop Java Applications for the Nokia 9210 Communicator?" at Forum Nokia web site (http://www.forum.nokia.com). You have to register first before downloading documents.
The document explains how to write a small Hello world application for the Nokia 9210 Commumicator. Different development guidelines are discussed and Symbian platform specific issues are explained.
As a final result developer can launch the application by using self-made icon in the Extras screen.