What features can I use without adding a data plan?

In general all applications which don't require data transfer over network. In addition some applications use data connection for extra features but basic functions can be used without it. For example you can listen music stored to your device without data plan, but for accessing web feeds or Nokia Music Store, data plan is needed in case WiFi connection isn't available. Also Nokia Maps can be used without a data plan in offline mode. In that case you need to download map data to your device memory over WiFi connection or by using Nokia Suite.