iphone 4 7.1.2 softbank japan network lock

pls help me guys to solve my problem on how to activate again my iphone 4 l softbank japan network lock. after i did a factory reset i can not totally use my iphone coz it only stock on HELLO, sim card required. i can not also use the i tunes to restore my device coz the itunes just display sim card required disconnect and insert a valid simcard. but before i resetted my device it really works and no problem at all. i was not able to use it as a smart phone but i use it as my ipod. and how to unlock it since i find in the internet with the different unlocking websites but so very expensive. anything you knw how to network unlock it with an affordable price pls let me know. thnx... and more power to all