I was on a cruise ship in the Caribbean a month ago and needed to keep in touch via email.
Connect@sea offered a 300mb plan which I thought would work. I followed all of their guidelines about what to disable etc.
All was going well until…
I woke up on day 3 and IOS 8.1.1 had downloaded (182mb) and was ready to install. After the 182 mb download, my wifi package was also empty.
I can't find any way that I could have prevented that large automatic download. Is there a way? (It's true that it doesn't install until you approve it, but it downloads automatically.)
Suggested in the first answer is to only connect to wifi, download email and disconnect. That method won't work for me. Some of the emails are server generated alarms (I also kept push notifications from the Pingdom app enabled), therefor I was unable to disconnect from wifi except when checking email because I need the email to arrive in real-time.
What are the best practices when you take your iPhone with you on a cruise? (it wasn't easy at all actually, there are a lot of controls to use when you don't want to use cellular data, but everything is designed to assume that WIFI is a giant unmetered pipe—not a restricted connection that you don't want to suck data from.)
Best Answer
Regarding the OS update, I seem to remember that filling the iPhone with (songs, books, pictures, apps) to the point where the OS update would not fit was the only way to prevent the OS update from downloading. On a cruise, where you would likely be taking many pictures, etc, this is not a very amenable solution.
When I've had metered WiFi in the past, I would turn it off except when checking mail and then turn it back off immediately after downloading all the messages. Depending on how fast your WiFi connection is, even this may or may not have prevented the update from downloading.
About the only thing remaining is to ask the network admin onboard the ship if they could block the software update site as if it were a torrent or porn site.