As many other uses who have iPhone 3G and updated to OS4 noticed that their phone after some time is almost unusable or this. I have installed SBssetings which shows me free RAM and i noticed when RAM is lower 10MB phone doesn’t respond and can’t work properly. (Some memory leak ? not sure)
So I have decided to downgrade to 3.1.3 and it is not as easy as you would thought.
I want my phone to be jailbreaken so you have 2 options:
1. find already customized firmware (search for customized restore firmware)
2. customize firmware yourself 🙂
Everything was ok, except that I got error 1600.
I have solved this issue by setting iPhone NOT in DFU mode but in RECOVERY mode.