So to be clear, and it wasn't clear to me at first, there are two related but separate systems here. If you are interested in the details, read on!
The Disney Navigator App, connects to the DCL_Guest WiFi, and doesn't use any of your WiFi data, free or otherwise. Before you get on the ship, the App is just a countdown clock. After you get on board, and connect to DCL_Guest, a lot of other features unlock. One set is the online navigators, which let you see all of the activities on the ship for the rest of the cruise. This is great if you have to miss something, to see if it will happen again later. Likewise, you can see all of the menus for the rest of the trip. This is also very helpful if you want to choose an entree, based on what your choices will be tomorrow, etc. Third, and perhaps most importantly, is the chat function. This allows you to talk to other people on board. They have to "accept" you first, so at first you'll be having to find and "request" contact with the rest of your party, once you do, you are all set. Like regular chat you can set up multiple threads with different combinations of people, so one for your whole group, one for just your spouse, one for just your kids, etc. We had nine in our group, so this was a great way to find out who was doing what, or where to meet for lunch, etc. It doesn't beep or vibrate when you get a message, so you will have to check it periodically, but it becomes a habit. All of this is free and consumes no wi-fi data you may have paid for. Also, it works with any (most) wi-fi capable apps. My 12 YO niece didn't have a smart phone, but she had a second-hand iPod touch, and that worked fine for the app.
The second thing is the 50 MB of free Wi-FI. This you have to sign up for, using your phone, once you get on the ship. Before you do, you'll want to turn off all of your background apps and automatic downloads, or it will eat up all of your free data in no time. If you aren't sure how to do that, I've read here that you can get help from Guest Services on the ship. Mostly, make sure you log out of it whenever you aren't using it, so it doesn't accidentally use your data. You can still use the Navigator app, as it is separate. Once you are ready for your free 50 MB, there are instructions in the first Navigator you get on exactly how to get it. Reports differ on if it is 50 MB per cabin or per person. We were able to get 50 MB for my wife and another 50 for me. We both stated our name and cabin number, so we weren't trying to trick the system, all it asked of us was to provide different e-mail addresses, which we did. You must do this before midnight on the first night to get the free MB. You can buy MB any time you want, but they are in non-refundable bundles. So if you buy 1000 MB, but only use 150, no refund. On the other hand if you buy 100 MB, and then end up needing more, you have to buy a new package. So, for instance, 10, 100 MB packages cost way more than 1, 1000 MB package, so it is to your advantage to make a decent guess as to how much you are likely to use (ballpark) and buy the appropriate package.
