As long as your parrot has a balanced, healthy diet, cuttlebones, gravel, and grit are NOT necessary. There have been reports of crop impaction in some parrots due to feeding them these items. Ensure that your food provides proper amounts of calcium (which high quality pellets generally provide).
Some additional information: "Grit or gravel (which is made of from rock, sand, oyster shells etc. in many wild bird’s diets), is there to provide the same service that is accomplished by our parrot’s ventriculus, or muscular stomach. Since parrot’s also hull their seeds and nuts and eat only the soft inner parts, gravel is NOT a requirement in their diet. It is simply an unnecessary aid to breaking down food and can actually cause harm to the digestive system. Unfortunately, it is sold in many pet stores without any warnings as to it’s hazard to parrots."
A website with more information:
http://eclectusparrots.net/grit.html