Update
 

How can you update the firmware on a jailbroken iphone without having to re-jailbreak?

Re: Update
 

Great question, I was wondering the same. I "think" the answer is... you don't. I'm not touching mine until I know for sure that updating won't break it.

Re: Update
 

Unless you have it on a service other than att you can always jailbreak again after you update, but if you do have it on another service it will mess it up pretty bad. i saw something in cydia once, but i cant find it again.

Re: Update
 

If you update the firmware you will need to rejailbreak it. But there is way to not loose any information.

First - installed APT Backup from Cydia (if you don't already have it)
Second - run backup in APT Backup (this will create a list of all the cydia items you have installed)
Third - perform back of iPhone in iTunes
Fourth - update firmware
Fifth - jailbreak phone
Sixth - install APT Backup from Cydia
Seventh - Restore from back in iTunes
Eighth - run restore in APT Backup

I know this may seem complicated, but I have updated firmare for 5-6 phones via this method and it works 100% of the time.

**Note 1: What APT Backup does is makes a list of your Cydia items. When you do the restore it hits Cydia and redownloads that list, so it may take a few mins depending on how much stuff you have grabbed from Cydia.**

**Note 2: If you use Categories, you may not see the items you have in the categories until after you have ran the restore in APT Backup and categories get downloaded**