How to unlock an iPhone 4s from Sprint for use on another network

Thanks. I did contract Sprint first. Over the phone they said they could unlock my iPhone 4s, but here is their email reply several days later: " Sprint is unable to unlock your phone due to programming restrictions on devices manufactured before February, 2015. You can try providing your master subsidy lock (MSL) code 627588 to another carrier to find out if it will work on their network." I suspect they are upset that I am trying to move to another carrier. Thanks

Thanks. I understand. I was just looking to advice from the Apple community on how to unlock the iPhone without the help of Sprint. Thanks