Is there a better way to unlock?

[Wilhem_Scream]

I have just gotten the code from T-Mobile to unlock the sim on the phone but it involves inserting and applying a sim from another company which will then be tied to the phone. Correct me if I am wrong on that but its what I was told. Now my question is how can I unlock it without having to add a carrier and how would I get it to be fully functioning? I have read that it will only have limited services on it and will get only a 2g signal. I am selling the phone and want to make it useful and worth buying to someone.