If you are still in a contract with your mobile operator, for example you were given the phone at a subsided price with a contract, then you may be in breach of contract by unlocking your phone (as the phone may still be considered their property).
However if it is a pay as you go phone that you have paid for you may not be in breach of contract (with your operator) by nlocking your phone, as the phone may be considered as your property. You should check the terms and conditions of your mobile operator before you unlock your mobile phone.
taken from the disclaimer page of the website!