Does the iPhone has a SIM card slot? Ensure if it is a GSM network locked iPhone. Then find put the network to which it has been locked to. Then visit Simpleunlocking.com and select remote unlocking service to unlock the iPhone. Also make sure that the network is available in the supported networks list. This remote unlocking service is safe, simple, affordable and quick. This is a permanent unlocking method and doesn't require a jailbreak too. Good luck mate.