Several carriers and service providers such as AT&T would not unlock iPhone 4s, unless you already are finished with your contract. If you really want to unlock your phone, then you may opt to end your contract earlier than what is said in the terms of the contract. For that, you may pay a fee. It would cost 249$ plus the remaining months’ fees. It would really cost a lot to end the contract. Otherwise, you may still opt to unlock the phone, without having to end your contract, as well.