I remmber that AIS, TRUE etc has a prefix you can use of 4-5 numbers to call abroad much cheaper (be is via the net I think)

Any one remember these codes please.

With the True Inter SIM, 00600 and 006. With any network; 009 is routed via CAT. 008 via TOT. DTAC also have 004.

And AIS have 005 and 00500.

http://www.ais.co.th/12call/en/service-ain.html

A calling card can also be used, you get free local access.

http://www.thaitelephone.com/EN/calling-card/thailand/catphonenet/index.php

http://www.thaitelephone.com/EN/RateTable/index.php

With True you have two services 006 is high quality, 00600 is budget

For example prices to the UK are 6 baht per minute for 006 and 1.5 baht per minute for 00600.

For the UK I always use 00600 which is always OK but for some countries such as the Philippines 00600 often gives a very had connection.