Someone commented in a Forum ..
"As with any upgrade to the iPhone Firmware, there has never been a way to upgrade any firmware with out losing your jailbreak. Here is my suggestion to you. I use a program called PKGBACKUP. You can buy it on cydia. this program creates a backup list of all your cydia installed packages. Once done you sync your iphone with itunes and that list gets backed up. Then you can re-jailbreak once the jailbreak for iOS 4 comes out. Reinstall PkgBackup. Restore your iphone's backup from itunes. Run PkgBackup and then you can reinstall all your cydia packages. I've used this in past in it has worked flawlessly.!!"
There is an article from Apple website on how to backup, update and restore your iPod and iPhone --> HERE
- Posted using BlogPress from my iPhone