This is a thread for both Android "rooting" and iOS "jailbreaking", why you should do it, how to do it, apps exclusive to root/jailbreakers, as well as a place to show off your rooted/jailbroken device. We had a previous thread about this a while back, but I decided that we need a newer thread with more information from someone who's used both iOS and Android quite extensively.
Disclaimers!First off, I'm not responsible for anything you do, this is simply a tutorial. I won't be held liable for if you brick your device while doing this.
Why you should jailbreakOn iOS, you're limited to things only approved by Apple, on their "App Store". Outside of that, you cannot run anything that requires manual access to the filesystem (for example, installing and playing Doom or any emulator). There's only one way to access the entire filesystem, and it requires becoming the root user. After you jailbreak, you get an app called Cydia, which is a third party app store. This allows you to install stuff that lets you modify your own device, and the possibilities are pretty wide after that. You can apply custom themes, remove system applications that you never use, make your iOS device unique and not like the rest.
On Android, you're not nearly as limited. You can install applications outside of the Android Market by default, install different home screens, and much, much more. However, there's still a perfectly good reason to root your device: custom Android ROMs. Most devices you get from carriers have unremovable bloatware (apps you don't want) or the ROM isn't fully optimized. There are plenty of ROMs made from the base of Android (referred to as Android Open Source Project ROMS or AOSP ROMS) that give you much more performance with a stock Android experience. On top of that, you can also use your device to wirelessly tether your laptop, something that can't be done without root. And again, you can apply custom themes, modify your filesystem, all of that.
How to jailbreak/rootFor iOS, you'll want to use the utility called redsn0w. It is compatible with all iOS devices that have been out on the market (except for the iPad 2G). Beware, on iOS, when Apple releases a new update, DO NOT UPDATE IMMEDIATELY. You will have to wait for a new jailbreak to be developed for that version of iOS, as Apple will try to patch it up.
For Android devices, it varies depending on what version of Android you're on, and sometimes what device.
For devices running Android 2.1, it seems to be completely dependent on what kind of phone you have. I can't find any info on an "all-in-one" way to root 2.1.
For devices running Android 2.2, you'll have to download and run the application
"Z4Root" on your phone.
For devices running Android 2.3.3, you'll need to download and run the application
"GingerBreak" on your phone. (You might need an XDA Developers account to download that file).
Things exclusive to jailbroken iOS users:WinterBoard, an app that can theme iOS (Cydia)
MobileTerminal, for terminal access (Cydia)
Glasklart, a transparent theme for WinerBoard (Cydia)
iOS4 Features (iPod Touch 2G only, Cydia)
SBFlasher (Cydia)
(help expand this list by suggesting stuff)
Cydia repositorieshttp://phajas.xen.prgmr.com/repo/Things exclusive to rooted Android users:CyanogenMod, a custom, highly customizable and feature-packed AOSP ROMROM ManagerWireless Tether for Root Users (Android 2.2 only)AndroSS, an easy utility for device screenshots(help expand this list by suggesting stuff)
Your turnShow off your jailbroken/rooted device (don't forget to include screenshots and device info like specs and what ROM you're using), suggest things for both jailbroken iOS and rooted Android, and ask questions about jailbreaking/rooting.
