Roaming is very convenient but can become very expensive.
To reduce my roaming charges I use sim2fly service from AIS:
You buy a prepaid sim card and add credit as needed. To avoid having to change sim cards when I travel I use a dual sim mobile phone.
Before leaving thailand I transfer my normal mobile number to my sim2fly number so I’m reachable and don’t pay huge roaming bills.
Being a prepaid service I know I won’t pay more than what credit I have activated on my account. You can add more service with credit recharge that you buy before leaving thailand (at 7/11 or other convenience store) or use AIS website to buy more credit while abroad. ( alternatively, someone in Thailand can buy credit recharge for you)
If you want data roaming then you can buy special prepaid packages depending of the duration of your trip and your destination.
You then don’t have to worry of huge roaming bills (actually I don’t have roaming enabled on my normal mobile phone so no worry about that)
Please post your comments and questions if any.
Enjoy your trips.