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There are several things you can do get your phone working on those places. Call your carrier network and ask them about international roaming plans. So you can get messages, calls etc on that country. Without an international roaming plan, you will not be able to make or receive calls, messages and use internet. Remember, roaming plans and charges are very costly.
Also, you should contact your carrier network and ask them to unlock your phone, so you can use local SIM card in those places in case if you don't want to activate costly roaming plans or prefer to use the networks in those places. If your phone is not locked to any particular carrier or under any contract, then it is probably already unlocked. But you should call your carrier network to make sure it is unlocked. They can unlock it for international uses.
These are the only things you have to do before leaving your country.
If you have any questions or would like any additional information, please don't hesitate to ask.
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