I have tried a couple of these providers and yes, they are very cheap, but I have found the quality of the connection has most times been terrible from the UK. So, for anyone in the UK, I suggest you buy a 'mobile world' sim card from carphone warehouse and use your mobile phone to call Thailand at 15 pence a minute. It's also worth taking a look at www.moneysavingexpert.com run by Martin Lewis. There are some great suggestions about using mobile phones to phone abroad, and if you are on a monthly plan, I believe that it's also possible to phone 'for free' using your inclusive minutes with some networks.