I have been travelling actively since 2005, especially to Thailand. Previously, whenever I was overseas, I put my Malaysian phone on roaming. And the phone bill used to cost me a bomb. In the past when I took leave and visit Thailand, between 9 to 16 days per visit, my local phone bill used to cause almost RM300. Once, spending just 5 days in Sri Lanka and 3 days in India cause my phone bill to spike up to RM400 plus.
Then in July when I spent 2 months in Thailand, my friends there taught me to get a SIM card and an international calling card. With a local Thai SIM card, you can buy an additional International calling card that allows you to call home at a much lower rate.
Here’s how:

1. Go to the nearest 7 Eleven to obtain the following:
a. A 1-2 Call SIM Card that cost between 50 baht to 100 baht. Take note that this is no refundable but the SIM card gives you a local Thai number that you require to make calls (both local and overseas). However, you still need to buy the top up card below before you can make any phone calls.
b. Top up 1-2 Call cards: depending on how long you stay there, a 50 baht will last you for 5 days and 100 baht will last you for 10 days. So if you are staying in Thailand for 10 days, then buy the 100 baht top up card (the green card shown on the top diagram). If you did not top up after the specified time, then you will not be able to make any outgoing calls or send any sms.
c. International calling card. I was told that Hatari’s phonenet is one of the best rate around. It cost about 4 baht per minute to call back to Malaysia and some other selected countries. By buying a 500 baht card, I could call back home for a total of 2 hours.
It is assumed that you already have a mobile phone on your own. Just replace the SIM card with the 1-2 Call Sim card.
At first, I had problem buying the international calling card on my own because the staff at 7 Eleven did not understand me and gave me an international phone card that is used for public phone. Therefore, please remember to state that you want the Hatari Phonenet card. They are normally sold in denominations of 300 baht or 500 baht and sold at 7 Eleven. The International card is valid for 6 months from the time you first used it.