I've recently jailbroken my iPhone 4 with 4.2.1 and now it has baseband 3.10.01 using redsn0w. I need to unlock it so I can use any simcard. As far as I know, there is no unlock even with ultrasn0w for this baseband. I was wondering though, if it is possible to downgrade the baseband to a version where unlock is supported. Thanks for reading this.