That’s a common question asked by new jailbreakers, and a challenging one to articulate by master jailbreakers. The latest version of redsn0w 0.9.6b4 will jailbreak your iOS 4.2.1 device–but depending on which device you have, your jailbreak will be either tethered or untethered.
Here’s the following explanation from the iPhone Dev Team:
Update #2: Â The notion of a â€œtetheredâ€ jailbreak is pretty new to many people, so hereâ€™s a quick rundown on what to expect:
- If youâ€™re on an iPhone3G, old-bootrom iPhone3GS, or non-MC ipt2g, life is easy. redsn0w installed an untethered jailbreak and so nothing below applies.
- â€œTetheredâ€ does not mean you cannot boot at all without PC/Mac assistance. Â If you have not installed any tweaks that hook into important programs like SpringBoard or CommCenter, your device will actually boot. However, jailbreak programs like Cydia wonâ€™t work (and Cydia may still have a white icon). Â Also, certain built-in apps that had to be moved by Cydia will fail (Safari being the most noticeable example).
- If youâ€™ve installed MobileSubstrate tweaks that hook into SpringBoard or other important programs, your boot will actually fail (youâ€™ll get stuck at the Apple logo). You need to use redsn0w to â€œJust boot tethered right nowâ€.
Remember, @comex and others are working on a way to untether the 4.2.1 jailbreak. Meanwhile, the above 3 points hopefully will make it all seem less confusing
A tethered jailbreak is not fun to have when installing tweaks via Cydia. Any reboot will result in your iPhone requiring a Mac/PC to activate it again. Imagine yourself on the road and your iPhone is rendered useless. Not fun. An untethered jailbreak is in the works, but it will take some time. I’m going to wait it out for my iPhone 4.