An unbricked iPhone 4S with a new Prepay MicroSim must be unbricked using iTunes on a PC, Mac or laptop, and cannot be unbricked using the 3G option available on iPhone 4S.
Attempting to unbrick a new Prepay Microsim using 3G will result in all data on the handset being blocked.
Unbricking with existing active Prepay SIMs and new / active On Account SIMs is able to be completed using either the iTunes or the 3G options.