I was the original poster who asked the question and I'd like to follow up by saying the app worked great! It's kind of tricky to set up the text feature. You have to search for fellow passengers, then scan their QR code to add them to your list of contacts. Once it's in there, it works great. You get a notification sound when a message comes in, and they come in within a few seconds of being sent.
We did not purchase an internet package, we just used the free wifi to operate the app on the ship and on the island. I also enjoyed planning my day by scrolling through the activities and "adding" them to my personal agenda. The app sent me a reminder notification 30 minutes before each even, just in case I forgot. I liked that feature as well.