The Java Application runs on your phone, allowing you to store and update lists in the memory of your phone, so that internet access is only required when synchronizing. . This means that you can view and update your lists when there is no signal.
You could access the Web Server version of the lists using your phone Browser, but this would be much slower, and involve alot more traffic over the internet, that, depending on your contract etc, would incur charges.
To run the Java Application your phone must meet certain requirements.