Jailbreaking Q and A
Q. If you have to restore your iPhone do you need to jailbreak again?
A. Typically you will need to jailbreak your iPhone after a restore. The jailbreak is a software modification to the iOS or the boot loader, these are typically restored to "factory" state when the iPhone is restored, thus eliminating your jailbreak. You can upgrade your iPhone using jailbreak tools such as PwnageTool to prevent the loss of your jailbreak. There are also several Cydia tools you can install before upgrading, to preserve your jailbreak (only available iOS 3.x).
Q. How do you get themes to work when you jailbreak your iPhone?
A. Once the iPhone is jailbroken you will need to download Winterboard. This application can be downloaded by opening Cydia and searching for the term "Winterboard". Once you have downloaded Winterboard, you may then download themes and install them on your iPhone. Open Winterboard to select and apply the specific theme which you desire to use. For more details on how to get themes working, read the free iPhone themes guide.
Q. How do you unlock the iPhone once it's jailbroken?
A. There are several different methods of unlocking the iPhone once it has been jailbroken. Most methods involve using a computer based program and depend on the iPhone's baseband version. For older versions of the iOS, a program can be downloaded from the Ultrasnow Cydia Repository which will allow you to unlock the iPhone. Check into programs such as RedSnow for unlocking the iOS 4.
Q. Does jailbreaking the iPhone void your warranty?
A. The answer to this question is mixed - yes and no. If you send your iPhone into Apple for service and they see that it has been jailbroken, they will not service it. If the iPhone incurs physical damage and is not operational, they would not likely be aware and therefore service the iPhone. You could also restore the iPhone before sending it to Apple, thus returning it to a non-jailbroken state and therefore your iPhone would be serviceable by Apple. Find out if Apple Care is worth purchasing.
Q. How do I install applications from Cydia?
A. Once your iPhone is jailbroken you will need to use Cydia to install applications. Cydia allows you to find applications by name or search by category type. Learn how to use Cydia here to find out how to take full advantage of the applications and sources that are available.
This may not cover all of the jailbreaking questions, however, this likely answered the most common questions related to jailbreaking. The art of jailbreaking constantly changes and therefore you should always research before installing or updating your firmware.