What does the "EU Internet" switch do on my iPhone 5s? I have an iPhone 5s. I recently noticed that my Settings/Mobile page has a "Data Roaming" switch and an "EU Internet" switch:



The first I understand (enable data when roaming in foreign countries), but what does the second do? If I disable "Data Roaming", the "EU Internet" switch is greyed out. I assume it's related to the EU roaming regulations, but what does it actually do? Restrict data roaming to those countries?

In case it's relevant, my SIM plan is provided by Three UK. I have a plan with Feel at Home, (which allows me to use my data/call/text allowance for free in 16 countries - not necessarily EU ones though).
I believe it allows data roaming, but only within European Union countries. See http://www.cultofmac.com/288360/europeans-new-roaming-options/:

Inside cellular settings, Apple has added a dedicated “EU Internet” switch alongside the existing data roaming toggle. It gives users the ability to active Internet connectivity when they visit countries inside the European Union, while in other parts of the world in will remain inactive.
Presumably, this change follows new European legislation that says carriers can no longer charge customers for data roaming when they visit other EU countries. The rules don’t officially come into effect until 2015, but a number of carriers have already begun abolishing roaming fees.