Avec cette méthode d'ailleurs :
NOTE: THIS IS FOR 3.9BL ONLY
To do a full baseband and software downgrade:
1 -Put iPhone into DFU mode (if you are not sure how, use ziphone)
2 -Click Shift + Restore in iTunes and select the 1.1.3 firmware
3 -At the end, iTunes will give error 1015. Thais a good thing

it means the OS downgrade was successful. Use ibrickr or independence or whatever to get out of recovery mode.
4 -Jailbreak using ZiPhone GUI. Click the boxes for Jailbreak and activate (and SIM unlock if you wish) and click whatever button starts the ZiPhone process (varies from windows to mac etc)
5 -Go into settings -> general -> auto lock and set to never
6 -In installer.app add the source
http://www.appledailytimes.com/installer7 -Go back to the install tab. There should be a category called "Apple Daily Times"
8 -Go into the Apple Daily Times category and install the baseband downgrader you need.
-(If there are any errors let me know by emailing me:
william@appledailytimes.com9 -Wait a while as the baseband is downgraded
10 -Done!
If you are on 1.1.4 and want to stay on 1.1.4 but have the 1.1.3 baseband:
-Start from number 5 in the guide above
AGAIN, IF THERE ARE ANY PROBLEMS, PLEASE FEEL FREE TO EMAIL ME:
william@appledailytimes.comPS : j'ai juste un peu modifié le texte pour le rendre plus clair.