What is the best way to go about using my iPhone 6 internationally?

I will be spending 5 months traveling through China, Vietnam, and Thailand and am wondering how I should use my iPhone 6. I've read about international SIM cards a little, but not sure how they work. IIm trying to find the cheapest way to have texting, calling, and data capability.

If your phone is unlocked you could use local SIMs from the carriers in the countries you are going through. If not you'd have to resort to roaming which would be pretty expensive or just stick to Wi-Fi use.

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