Sim Unlock Motorola Tfc139b How Do I Unlock Motorola W156 So I Can Put In Any SIM Card I Want?

How do i unlock motorola w156 so i can put in any SIM card i want? - sim unlock motorola tfc139b

I received a free Motorola W156 and I give my 4-year-old son so that he can call me if theres an emergency, but it seems that the phone is a closed network? I tried to call a SIM-card and insert a code? I am a newbie so any help would be greatly appreciated ...