U need to contact sprint wherever your phone is locked to...lets say sprint USA. And tell them you are out of the country and you would like to use your phone in Zimbabwe. They will unlock your phone and it will be carrier free. Then you can flash new rom if you need to. Just make 100% sure the rom is for S2 Epic 4G ,otherwise you might brick it. As long as the account that the phone was attached is paid and nothing is owed sprint will happily unlock your phone. It will take a few hours.
Good luck