I am helping my friend to unlock a iphone 3g. I realize that it is on 4.21 firmware, modem 5.15 and bootloader is NOT downgradeable. The only choice to unlock this phone that I know of would be to go to 6.15 ipad baseband. I KNOW this is the kingdom come of iphone, no chance of going back. I heard story that if i updated to 6.15, there is chance that the gps would stop working and another rumor claim if I downgrade the phone firmware to 3.12 and with baseband of 6.15 and the gps would still work. Can ANYONE confirm it?