If you are traveling to thailand another good option is the story sim card. This will set you back £30 and you will get £25 credit. the story sim card is also known as a roaming sim card.
This story sim card is free to receive calls in over 80 countries. Check out the story telecom coverage for receiving calls and making calls while in Thailand.
Again this is a pay as you go sim and not one of the sim contracts that are more popular in the UK. If you want you can set the story sim card to auto topup. This is a great idea and you can set this that it will auto top up when you credit reaches £3, ensuring you dont run out!
If this is not for you check out what we feel is the best sim for thailand.