When you go abroad and make calls, send texts to the UK or elsewhere, or use data you're doing something known as roaming.
Each country has its own mobile networks with different contracts in place to let visitors use their services. This means that prices can vary significantly depending on your destination.
There are 6 different roaming zones throughout the world for calls and texts, and 6 different roaming zones for using data abroad. This means that your charges differ depending on which country you're in. It's also really important you know that you'll get charged for receiving calls aswell as making them when you're abroad.