Best thing to do with iPhone in vietnam?

Going travelling for 6 months or so, don't know what to do with my iPhone 5. I'm terrible when it comes to technology. What's the best option for me to continue using it over there, to access internet etc without costing a fortune? I'm from the UK if that makes any difference.

You can use it if there's Wi-Fi. Also install Viber and with Wi-Fi, you can call/text free.