I always turn off data roaming and 3G when I travel unless I buy unlimited package from AIS. I use an iPhone but operator always warn me after disabling data roaming and 3G its best to turn off the phone and then turn on again and double check again if both are disabled. So I formed a habit, I will disable everything before I turn off to board the plane. Then when I arrive at my destination I will turn on the phone as usual and then check again of both 3G and data roaming is off. However most of the time I purchase packages from AIS like this trip now to Taiwan I bought a 5 days package for I believe its 1200-1300 baht unlimited. I understand if single day is 350 baht per day. Oh I forgot in Japan as iPhone can be use there but ZI need to leave the 3G turn on as without 3G the phone cannot work.