Users relying on software carrier unlock ultrasn0w must use sn0wbreeze created custom IPSW firmware to upgrade there iDevice to an upgraded iOS version without updating the baseband which breaks the unlock. However, Apple iTunes prevents users from upgrading or restoring to these custom IPSW files and errors out the process with codes 3194 and 1600 - for which we have shared solution earlier. Here is an step-by-step guide to restore an custom IPSW file to iPhone using iTunes the correct way without any errors.