Mary, I have done this many times thoghout my travels and I can offer you these suggestions. You will basically have two options. If you are not interested in making phone calls and just want to take photos and email some to friends, as you depart for your trip, swipe the control panel up from the bottom of your phone and first turn Airplane mode on, then also on the control panel next to airplane, turn Wi-Fi on as turning AP mode on would have disabled it. So you basically end up with AP on and then Wi-Fi on in that order. You need to leave these settings like that until you return home, and at that time simply disable AP mode. With these settings you will be able to log into the ship's Wi-Fi and any other network as you please. You will not incur any cellular or data charges from your carrier. Please be aware that most ships rely on satellite connections which are slow and expensive. They will charge you for your Wi Fi access although some high end lines include it in their fares (the exception). This is common on cruise lines throughout the Med and river boats have better access due to proximity to land. So while you can take pictures any where in this mode at no cost, sending them from the boat may not be your best choice, particularly if you have a large amount of high MB files. While in port of course, you can access local networks and that is what I recommend. Usually if you follow some of the crew, they make a bee line to the best public Wi Fi in the area as they are familiar with each port and are eager to talk to family.
If you want to make calls, which I doubt from your post, you would need an unlocked phone (if you bought yours at an Apple Store it is unlocked) and then you need to purchase a SIM card that is valid for the areas you are visiting once you arrive there. Airport kiosks are a good source and Vodafone a popular choice. If you want to do this, please post back and I will give you the instructions.
Enjoy.... wish you could send me some of the pictures.
elcpu