Standard field Contact.REVISION (PIMItem.DATE type) is not mandatory in implementation (may or not be implemented),
Its not implemented on Nokia devices (according to Java Developers Library docs implementation notes to that jsr) and its not present on device I've tested
However I've already read two threads on java section from which it seems it could be useful for client<>server synchronization using standard apis like http-based connections and that JSR, especially that Nokia implementation seems to support Contact.UID field (PIMItem.STRING) - having both fields it could be probably easy to write client side api for synchronization with other tier without using any other client-side api,

Reading Motorola pdf about j2me development it seems that they have that field implemented (implementation varies in details),