If its unlocked then all carriers works without any problem. If its locked then you can make unlock request here they will surely unlock it for you. https://www.att.com/deviceunlock/? If nothing works i can unlock it for you for a small fee.
Its a big responsibility and technical implementation. If you have no idea on it then better go for other choice, or financially help a project. Anyways here is some video parts you can refer.
I don't know why the donation amount still the same even the value varied a lot. Why they couldn't make a lower amount which attracts many members in to the status.