At this point, the only way to downgrade an iPhone/ipod is if you've already run the previous OS and Cydia's managed to cache these things called SHSH blobs.
Basically, a while back, apple starting "Verifying" every restore with their servers, so when you try to restore, it calls home with your iDevice's serial number and gets back an encrypted key that tells itunes whether it's ok to restore to that OS or not.
If you've run Cydia on the older OS, the dev put in some code that pulled out the special response-key and stored it to his server, that way you can restore back.
tl'dr: No you can't downgrade an iPhone 4 or an upgraded 3GS
As far as reasons to jailbreak 4.0, mainly, I have an iPod Touch 2G so it lets me enable the multitasking. I run Music Controls(Swipe controls on the lockscreen among other features), DTunes(if my home internet's shit and I need to torrent something on the go), some apps that make good use of the lack of restrictions on hooks(Flashlight, it automatically brings up the brightness to full while it runs), SBSettings(Controls for Bluetooh+Wifi+Brightness from any app), I hide stupid built in apps like Stocks with SBSettings, finally, I made a whole bunch of tweaks to make everything run faster in general.
Depending on what exactly goes wrong with your iPhone, as long as you can DFU and restore it to a non-jailbroken OS, Apple won't know the difference, so it kinda coids out your warranty but they won't know any better. There are only 3 actual ways to brick an iDevice, and you have to pretty much specifically try to type in a string of commands into mobile terminal to do it.
P.S.
SonderKommando wrote:
rammunition wrote:
so whats the best option, downgrading to a different firmware? if so which one?
If you can find it and install it without bricking the phone. or wait... itll get hacked soon enough. I was able to downgrade firmware once, Put the device in recovery mode and then restore through itunes. I forgot how to be able to choose the firmware version, google it.
You hold down OPTION (on a Mac) or SHIFT (PC) and click the Restore button in iTunes, it lets you browse to find your older/jailbroken OS file. (See above about SHSH blobs though.)
Last edited by TheDonkey (2010-07-22 01:18:34)