With a mobile phone the caller doesn't know where you are when they call. So if you are international then you pay the international cost of the call or SMS (if you answer).
A travel pack gives unlimited calls anywhere (made and recieved)
You might also investigate an app like whatapp that allows free sms and calls using data only. You can usually purchase a local SIM with a big data allowance that you can use overseas.
Travel Tip: Google maps can save large areas onto the phone. Do this before you leave over wifi and you will have access to maps data free while travelling.