You may have heard at least one of these mobile terms before: jailbreaking, rooting, and unlocking. They're often used interchangeably, since all three are device hacks that free your phone (or tablet) to do more things than you normally could with it. However, unlocking isn't the same as jailbreaking or rooting. Here's a basic introduction to these methods and the reasons why you might want to jailbreak/root and unlock your mobile device.
What Are Jailbreaking and Rooting?
Both jailbreaking and rooting are methods to give you unrestricted access to your mobile device's entire file system. The difference between jailbreaking and rooting is jailbreaks refer to Apple iOS devices (iPhone, iPad, iPod touch), while rooting refers to Android devices. It's basically the same thing, but different terms for the mobile operating systems.
For Android devices, you can think of a tree metaphor: rooting gets you to the bottom or root of your system. For iOS devices, you can think of the "jailed garden" metaphor often used when talking about Apple products: jailbreaking gets you past Apple's restrictions on your device.
Why you might want to jailbreak your iPhone/iPad or root your Android device:By rooting or jailbreaking your mobile device, you have greater control over it. After a jailbreak/root, for example, you can install apps blocked in the App Store or Google Play, such as tethering apps to turn your phone into a modem for your computer. Jailbreaking and rooting get you access to a greater range of third-party apps and tools, e.g., with Cydia, an alternate apps manager for iOS devices.
Other reasons to jailbreak or root include: upgrading your mobile operating system version before it's available through an over-the-air-update, loading a custom ROM (Read Only Memory) on your phone (replacing the preloaded OS and apps on the phone with a customized one), and completely changing the overall look of the device with custom themes/ROMs. Rooted and jailbroken devices also often have better performance and battery life.
Cons of rooting and jailbreaking: There are some risks involved with jailbreaking and rooting. For one thing, these technically void your warranty, so if something's wrong with your phone after you jailbreak or root it, the manufacturer won't honor the warranty to fix it. Another issue is that your device can be more vulnerable to malicious apps and you can possibly harm your device during the rooting or jailbreaking process. The solutions to those two issues is to be very careful about what you install on your phone (something you should be doing anyway) and only use rooting and jailbreaking methods that have been thoroughly tested for your device and operating system.
Note: Jailbreaking and rooting, while they void your warranty, are not illegal.
How to root or jailbreak your device: Although they might seem like scary, complicated methods, jailbreaking and rooting are fairly easy to do, with tools like JailbreakMe and SuperOneClick. For Android phones/tablets in particular, you'll want to make sure the rooting method is compatible with your particular device (check the XDA Developers forum for SuperOneClick or Lifehacker's guide to rooting Android phones). Also, before doing any of these methods, make sure you've backed up your device or at least saved all the important data on it, and have it fully charged and plugged in.
What Does It Mean to Unlock Your Phone?
Like jailbreaking and rooting, unlocking your phone gives it more freedom and flexibility. While jailbreaking/rooting gives you more access to the device's file system, unlocking lets you use the device on other wireless carriers. Typically, cell phones are tied to just one service provider, so you can't use it on a different one, unless you buy it unlocked or unlock it.
Why you might want to unlock your phone: The primary reason to unlock your phone is to use it on a different wireless carrier. Let's say you really want an iPhone but are currently on T-Mobile and want to stay there; you can buy the iPhone unlocked from someone (it'll cost more than the subsidized, 2-year contract price, but you don't have to sign a 2-year contract) and use it on T-Mobile. Or you could unlock your phone before you upgrade to a newer model and sell it. Another reason is if you want to travel to an international destination and don't want to pay crazy data roaming fees; you could use a local prepaid SIM card with an unlocked phone (if your phone has a SIM card, that is).
Reasons not to unlock your phone: The biggest reason not to unlock your phone is legal: As of January 26, 2013 in the US, per the new terms of the Digital Millennium Copyright Act, it's illegal to unlock your phone without your mobile carrier's permission. Civil fines range from $200 to $2,500 per unlock and criminal penalties up to $500,000 and five years in jail.
How to unlock your cell phone: Rooting or jailbreaking alone do not unlock a phone--you need a separate procedure. To unlock your phone, you can ask your carrier or a third-party to do it (although, again, it's now illegal to do it without your carrier's consent). Other methods include using special unlocking software or buying an unlock code (if you have a GSM phone). GSM phones, which have removable small cards called SIM cards, are easier to unlock; AT&T and T-Mobile are the two GSM providers in North America. Some software methods require your phone to be jailbroken before you can use the unlocking software.
Many wireless carriers do sell unlocked phones or have unlocked phones upon request. However, with the new law, it's really up to the carriers to decide (and given that your purpose for unlocking is likely because you want to switch service providers, it's in their best interest to prevent you from unlocking it). Your best bet is probably to buy an unlocked phone directly from the carrier or vote against this ban and hope that bill to make unlocking your phone legal get passed.