onlyone is right : in every little thing there is a small amount of risk. but this is life.
this forum give you a big choice : you can buy log and unlock your phone, but he gives you too a tutorial here http://www.topsony.com/forum/showthread.php?t=23
with the main files supported by semctool 8.4 free: you have to write a supported main file and unlock and after write back your firt main file.

if all that is too complicated for you = buy a TMS log it's not too expensive:)