An anecdotal experience with this: My mom is currently on the Dawn. We both have iPhones. She only has her FAS minutes - not an unlimited plan. We have been sending and receiving iMessages in real time, while she is NOT logged in to her account - she is just on the internal ship wifi. We were both very surprised, as we did not expect that. However, I would imagine it's actually a mistake/oversight on how the wifi is set up, rather than something that is supposed to happen, and would not count on iMessage being readily available when not logged into your wifi minutes (or without using an unlimited plan).
We just got back from the Getaway and had similar experience. I could receive iMessages without being logged in. It seemed like I had to log in to send an iMessage, but now that I think about it, I am not sure I tired to use it without logging in - so maybe?
the key thing that is often overlooked here is that this only works if both parties are on apple devices. you can not send an "iMessage" to someone on an android device when connected through the ship's internet, whereas you can normally do just that while connected to the internet (off the ship).
We are on the Escape and my kids pointed this out to me as well. I believe it's because iMessages and Push Notifications come from the same place. Meaning that in order for their app to be able to send push Notifications telling you someone has sent you a message or anything else they need to notify you about, they have to also open up iMessage.
One thing I will say to contradict the above, we can send and receive without being logged in or using an internet plan of any kind. This does for some reason exclude pictures, but I'm perfectly fine with that.
iMessage (text only) worked fine for us (sending and receiving) on the Breakaway a couple weeks ago. Push notifications from other apps also came through. We had an internet package, but iMessage worked when logged out as long as connected to ships wi-fi.
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