In article , Charles
wrote:

If they have an iPhone 5 it is not likely they have an unlocked iPhone
on AT&T.

at&t will unlock it for international use if the customer is in good
standing, or the phone might be unlocked already, such as a verizon
version.

They won't unlock it unless it is out of contract. In any case
buying a local sim is overkill if they only want to use it for
emergency purposes.

buying a local sim is not overkill. they will undoubtedly want to use
the phone for more than emergency purposes, including calling
restaurants, tourist attractions, hotels, etc.

Text messages are the least expensive way of
keeping in contact on a cruise. They can also text when the ship is at
sea and on the ships cell service.

for incredibly ridiculous prices.