Make sure your Motorola phone is GSM (Global System for Mobile Communications). There is no reason to unlock a phone that is not a GSM phone, as only these phones can be used on different networks.
Make sure your Motorola phone actually is locked. To test your phone's lock:
Insert a new sim card.
If you get a message along the lines of "Enter Subsidy Password" "Contact Service Provider" or "Enter Unlock Code" then your phone is locked.