Only partially true, let's not be misleading. It works for short vacations, that's about it. The EU has a so called "fair use policy", that basically give mobile operators the possibility to charge you more when you're more than xx days out of the country of registration (it's more complicated than this, but it's the idea anyway). In my case, traveling often abroad, means I'm constantly hitting this limit which force me to buy local sim card from time to time. It's nowhere near like in the US if some were thinking at this for comparison.