When you travel outside your home country to another EU country, you don't have to pay any additional charges to use your mobile phone. This is known as "roaming" . Your calls (to mobile and fixed phones), text messages (SMS) and data use (web browsing, music and video streaming etc.) are charged at domestic rates, i.e. the same price as calls, texts and data within your home country.
The same rule also applies to any calls or text messages your receive while you're abroad - you aren't charged extra to receive calls or texts while roaming, even if the person calling you is using a different service provider.

Information about Roaming