The only way to do it is using BootNeuter.
First make sure you screenlock is set to NEVER!
On your jailbreaked phone - start installer and:
Add
http://scape-server.org/iphone to the sources in installer.
Then look under tools for BootNeuter.
Install BootNeuter.
Exit installer.
Click on BootNeuter.
It will detect your current settings.
If your phone was 1.1.2 firmware or newer then you need to go back to bootloader 4.6.
Select the 4.6 bootloader then:
Make sure that: Neuter, FakeBlank and Unlock are all OFF.
Then press flash.
DO NOT INTERUPT THE PROCESS OR YOU WILL BREAK YOUR PHONE.
DON'T Click on Home or Restore or anything.
It will take between 5-10 minutes.
When it has finished exit BootNeuter.
Connect to iTunes and RESTORE TO 1.1.4.
set up the phone as NEW. DO not restore from a previous backup!
Then activate using iTunes if your on an official contract.
*It may not ask you to set the phone up until after activation and if you don't activate it then it may not ask at all*
Thats how you do it! Good Luck!