Nailit, if you're likely to want to use your mobile while abroad, make sure that your package allows it and that International Calling is not barred, it will be difficult to arrange any changes while you are away.
The use of 'flight mode' is to prevent mobiles from interfering with planes navigation and communication systems. As you are going on a ship, you needn't bother with changing modes, just ensure that 'mobile data' is switched off.
Enjoy your break, you deserve it.