Inserting the SIM when you arrive in Thailand activates the SIM, and you should get a welcome SMS confirming your plan.
By dialling *101*9# [call] this displays your balance.
By dialling *102*9# [call] this displays your number.
It is not possible to use this SIM before you arrive in Thailand.
Using the SIM
There are no registration documents required. Simply put the SIM in your phone, dial any number, and your SIM is active. Comes with instructions in 6 languages. SIM can only be activated in Thailand, and will not work until the SIM in in Thailand.