I have a post paid AIS contract, and buy a data roaming package using the MyAIS app prior to traveling. You select the country you're traveling to, pick the best plan for you, tell it when you want it switched on, and away you go. The charge appears on your next phone bill. The ability to use messaging apps, and make free calls, including video ones, through them, plus receive emails wherever I go, makes the cost well worth it. On a recent overseas family trip, I bought packages for my wife and myself, and just kept my grandson's, who travelled with us, phone on flight mode, but with wifi enabled so he could do his internet thing whenever we had a hotel wifi connection. No extra charges at all on his bill, while knowing exactly what my wife and I would be charged on ours.