Yes, because releasing a phone has nothing to do with the contract of permanence, you have the duty to fulfill a contract with the operator but that contract can fulfill it with any other phone, or continue to comply with a terminal released.
The operator will never penalize you for releasing a terminal.

Yes, we can unlock the phone, even if it is blacklisted. But most likely after releasing it will not work with any operator, because if it is in blacklist as reported does not let call or receive calls with operators in the country. What I could do is; free the terminal to use it in another country, since the report does not affect countries abroad.

If the model is well selected, the original operator and the terminal does not have the software manipulated, the code must work.
Whenever the code is wrong, the money is returned, that is, in most cases we demand a video showing that the code has failed.

Yes of course, today virtually all GSM phones are quad-band, this means that your phone has an antenna with 4 frequencies that are compatible with all the operators in the world.

Of course NO, once the release code is marked the mobile memorizes forever that it must be free. Perhaps if it is taken to repair an official technical service it could be blocked, but simply by simply re-dialing the code it would be free again, and if you have not saved your code, we will send it back to you at no additional cost!