Originally Posted by enigmanic Yes, if you're already on 1.1.2, the only current solution at the moment is to downgrade back to 1.1.1, install oktoprep and upgrade back to 1.1.2.
Here's my step-by-step guide to downgrading from 1.1.2 to 1.1.1 using Windows. Please note that this is just a temporary solution, so that you can install the Oktoprep app and upgrade back to 1.1.2. (Big thanks to faseone for confirming that it works!)
Step 3. While holding down the shift key, hit restore. You'll get a prompt box. Choose the 1.1.1 firmware that you've just downloaded.
Step 4. Wait for the phone to downgrade. You will receive an error at the end and the phone will get stuck in restore mode. This is typical. Just exit iTunes.
Step 5. Start up iBrickr. Choose "Boot up Phone". This will kick your phone out of restore mode. After the process is finished, iTunes will start up again automatically.
Step 6. Restore your phone from a previous backup. After it's done, you won't be able to make any phone calls (since the baseband has been changed), but you will be able to use wifi. Using wifi, visit jailbreakme.com to jailbreak your phone.