This summer I travelled to Germany, taking the ferry to France, travelling to just outside Paris for a few days before then setting off through Belgium and Luxembourg to Germany.
Following issues with using data in Portugal last summer with excessive data usage on my iPhone, I followed the same process I had used last October when I went to Amsterdam.
So before we boarded the ferry at Newhaven, I went into Settings -> Mobile Data and turned off virtually all the apps which could use mobile data. Took me a while as there were a fair few. I turned off mobile data for virtually all my apps and also specifically iCloud Drive and iCloud Backup. I am pretty sure they were the culprits for my excessive data usage whilst in Spain.
As and when I needed to use apps, I either used the campsite wifi, or switched on mobile data for specific apps.
Arriving in France I was able to roam without any issues, of course as I travelled across Europe I switched networks, first in Belgium, then in Luxembourg and finally in Germany. In the end I used four different country networks. Each time I switched over without issue as I crossed the border.
In Portugal I reached 80% of my 12GB limit within the first twenty four hours. I did wonder if I would reach the fair usage limit on this holiday. As it happens I did six days into the trip, with two days left. It was relatively easy to purchase a 1-day Data Passport for £6 for the two remaining days of our holiday rather than pay silly prices for data on a pay as you go basis.
Though difficult to tell, I think the main data culprits were Waze and Amazon Music, which were used extensively as we drove across the continent.
