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.)