Just wanted to mention this:
We were on the Disney Fantasy for the September 2nd cruise that was rescheduled and shortened from Irma. (just got off on our way back home via hurricane Exodus)
The kids club sent a message through the app to my mum's cabin, but not to us? We did however get a message via our wave phone, but we had left them in our cabin. (Nothing serious, just siblings being siblings so the crew was kind enough to inform us)
However, our last 'day' of the cruise, which was chaotic, the cruise app suddenly without warning shut off. (No one was told this was going to happen. It could be automatically programmed once you hit a certain distance from the port, but we would still be on the ship for several more hours and not within cell tower range. Also, with everything else going on, I think there were more pressing matters that needed attention. Luckily, our kids were accounted for when it happened to us, but I know some fellow passengers who had to go searching for kids. ) Mine ended first, and luckily my husband was beside me, so we contacted other members of our party to expect the same thing. (The app wasn't great at adjusting for major scheduling changes - to be fair crazy circumstances. The app on my phone was having a hard time refreshing.) We dusted off the wave phones and used them as alternative communication for the rest of the time.
So, while the app is great, it was really nice to have a backup method with the wave phones!
They still have their uses!