If you are using AIS or any other Thai service provider, simply give them a call and then check with them if they have any tie-up with any telcos of the country you are visiting. If have ask them for unlimited plan and its very very cheap. How you think I online all the time in Singapore taking all those pics of MRT, Q'town and food and posting them immediately? Example of plan is AIS has tie-up with a telco in almost all ASEAN countries and also in Japan, Korea, Hong Kong etc etc rates is very reasonable and usually 350baht (1 day) , 950 baht (3 days) , 1400 baht (5 days), not $280 for 3 days come on. Its not just for business, if wife travel I will buy packages for her like her 2 weeks Japan trip I'll purchase 3 x 5 days packages which costs 3 x 200- baht = 6,000 baht (less than $250, for 15 days mind you). With the number of Viber and LINE calls and WhatsApp, Skype, MSN, LINE messages it very worth and not forgetting Instagram.
click here for - countries with Bridge Alliance having teh above standard rates I mentioned
http://www.roaming.ais.co.th/ais-ir-out-gsm-web/promotion-out-gsm25.html
click here for - other countries not on bridge alliance (like Japan and some European countries etc, some have unlimited plan like Japan and Germany and UK etc)
http://www.roaming.ais.co.th/ais-ir-out-gsm-web/promotion-out-gsm.html
This is the way to go of you are with AIS. Saves you lots of money.