How to Avoid Data Overage Charges When Traveling outside the US
Disable any apps that you don’t plan to use in Settings > Cellular. It’s tempting to disable only those that have used data in the past period, but it can be hard to predict when an app willdecide to retrieve a large amount of data. Be especially cautious about apps like Music, Photos, Podcasts, Dropbox, Skype, Google Hangouts, and Spotify that might want to stream media, sync data, or provide real-time high-bandwidth communication.
* To prevent email and calendar data from outside arriving on youriPhone unbidden, go to Settings > Mail, Contacts, Calendars > FetchNew Data, turn off Push, and select Manually in the Fetch section. The data will update when you launch the associated app.
* Also, in Settings > iTunes & App Store, turn off Use Cellular Data. To be safe, I’d also recommend disabling automatic downloads. Thatway your iPhone won’t automatically get downloads for purchases made by someone else in your Family Sharing circle, or those made on a device you left at home while you’re travelling.