What should I turn off in a foreign country (smartphone) to avoid unwanted expensive bills?

What do I need to turn off if i have a data plan? If I turn off roaming, can I still use wifi normally?

Sorry I don't really understand this stuff :(

Also iphone 4s vs nexus prime?What should I turn off in a foreign country (smartphone) to avoid unwanted expensive bills?
WiFi can still en cur you additional charges, phone up your service provider to clarify this with them, often this kind of stuff is 'in the small print'What should I turn off in a foreign country (smartphone) to avoid unwanted expensive bills?
It's only a bill if you answer it.