International roaming is when you connect to a mobile network in a country other than the one you live in. Therefore if you answer your phone using your regular SIM card while roaming you will be charged a per-minute rate (unless you have an international SIM that gives you free roaming in that country).
While you are roaming with a regular SIM card you are effectively being charged by two mobile network operators, hence the reason for using your phone abroad is so expensive. Smartphone users should also be aware of data roaming, if this is not switched off you are likely to come home to a huge bill as your phone connects to the internet automatically to keep you updated - don't make the mistake of thinking turning your phone off is a solution as this will not help!
What to do about it
- Firstly switch off data roaming and connect to free Wi-Fi in cafes and your hotel instead
- Set a limit with your mobile provider or get a pay as you go SIM
- Get an international SIM card for free-roaming and cheap calls, data and SMS, or if you do use your regular SIM always check the rates with your provider before you travel and try to send texts rather than make or receive calls