Un-tethered vs Tethered Jailbreak

[Source] - Un-tethered v. Tethered Jailbreak

If you have any questions regarding what a Tethered or Un-tethered jailbreak means, please read this first before posting any questions.

Tethered Jailbreak:

A tethered jailbreak ONLY applies to the iPhone 3GS and not all of them.

NOTE: I received an update that some iPod Touch2G and 3G require a tethered jailbreak, too. The serial number trick may or may not be in effect (I have not tested it), but the logic and practice is the same.

A tethered jailbreak means that once your iPhone is successfully jailbroken with blackra1n, you'll need to connect your iPhone to your computer if you ever need to reboot your iPhone or your iPhone loses battery charge.

What you'll see when you reboot your iPhone (if you're tethered) is the iTunes and USB picture. Once you get this, simply open up blackra1n and press "Make It Ra1n." This WILL NOT re-jailbreak or restore your iPhone, all it is doing is booting back up your iPhone for you.

You will require a tethered jailbreak if you have the NEW bootrom version. The OLD iBoot version was 359.3 and the NEW version is iBoot 359.3.2. There are a few methods to check which iBoot version you have.

Method 1 (Serial Number Method):

You can get a very good idea if your iPhone requires a tethered jailbreak by looking at the 3rd, 4th and 5th numbers in your serial number. If your serial number digits are "939" OR LOWER, you're safe. If you're serial number digits are "940" or HIGHER, you run a high chance that your iPhone will require a tethered jailbreak.

Some people are reporting that they've been able to successfully jailbreak without having a tethered jailbreak with a serial number of 940 and higher. While this is rare, it apparently is happening.

Method 2 (Using DFU Mode):

Windows:

1. Put your iPhone into DFU Mode
2. Right Click on My Computer > Properties > Hardware (tab) > Device Manager
3. Select the plus arrow for "Universal Serial Bus (USB) Controller"
4. Find "Apple Mobile Device USB Driver", right click and select Properties
5. Go to "Details" and find "Device Instance ID"
6. Scroll through the string and you'll eventually find the bootrom version (iBoot)
7. If it's 359.3 you DO NOT require a tethered jailbreak. If it's 359.3.2 you DO require a tethered jailbreak.

Mac:

1. Put your iPhone into DFU Mode
2. Open "System Profiler" and go to Hardware > USB (menu on left)
3. At the top right under “USB Device Tree Panel” click “Apple Mobile Device (DFU Mode)”
4. In the upper right corner look for the information “string on the Serial Number.”
5. At the bottom you will find the description BootRom version (iBoot).
6. If it's 359.3 you DO NOT require a tethered jailbreak. If it's 359.3.2 you DO require a tethered jailbreak.


Un-tethered Jailbreak:

This is naturally quite the opposite. You have an untethered jailbreak if you reboot your iPhone with no issues.