Welcome aboard! What an amazing way to spend your 25th wedding anniversary. The Fantasy is a gorgeous ship with so much to do, and so many updates from Disney's other three ships, you'll have so much to explore and take part in as you celebrate.
If you plan on bringing your own cell phone, laptop or other internet-ready device, you'll be happy to know that there is WiFi available in hotspots on the Fantasy. Your Personal Navigator will list the hotspots, so take a look at that once you're onboard. There are also internet cafes onboard, such as the Cove Cafe where laptops are available for you to use (for a fee).
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Internet and WiFi usage rates are posted on Disney Cruise Line's website. If you plan on using your cell phone, keep in mind that usage and roaming rates may be incurred while using these devices onboard or in the ports. You'll want to check with your wireless provider before you sail.
Our family always turns off our cell phones and wireless devices for the length of the cruise so that we don't accidentally incur a fee for downloading data. We love that going on a cruise with Disney is one of the only opportunities we have to "unplug" and get away from the demands and connectivity of our regular life. You might find that you're so busy (or so relaxed!) during your cruise you forget to go online, and I bet your children back home will understand!
Enjoy your trip and congratulations on such a wonderful milestone anniversary!