Unlocking an iPhone is often interchanged with jailbreaking. But they're not exactly the same. Jailbreaking is a procedure that's done to let you use applications that are not Apple-approved on your iPhone. However, before you can unlock your iPhone, you need to jailbreak it. Unlocking in this sense means breaking the lock on your SIM card and lets you use your iPhone with not just carriers that are approved by Apple, but with whichever network you prefer.
For example, Verizon and AT & T are the only networks with which you can use your iPhone. By unlocking your mobile, you can use other mobile communication networks in your local region or anywhere else in the world.
You have to be cautious, though, about this procedure, since it presents some risks. For one thing, there's a possibility that your phone can suffer damage while in the process of unlocking. Furthermore, you'll automatically void your phone warranty as soon as you have it unlocked. You can ask for technical support from Apple once you've done this.
Official upgrades for your iPhone will not be easy anymore to install once you have the device unlocked. For some cases, you might be able to install the upgrade, but running it on your phone will most likely become complicated and problematic.
However, your iPhone will still be functioning normally even if you've unlocked it. There is not any other unfavorable effect in its standard operation after unlocking. Your phone will still have the same features and functions as it had before you had it modified.
This procedure is often advantageous to people who'd want to use an iPhone, but are already in a contract with a network that's not associated with the brand. These people, of course, would not want to transfer to another carrier, since it would mean spending extra bucks for it. Sticking with their existing network contract would be more economic.
A frequent traveler usually would want to unlock his iPhone, too. They can use a local SIM card while they're in another country. With this, they only have to worry about local phone charges. It helps them dodge the steep international roaming fees when they need to call home to check in on their families or to clarify work-related issues in their offices.
If you're thinking of having your iPhone unlocked, make sure you read some more information about the whole procedure and its pros and cons. More importantly, be sure about the program or service that you'll use to accomplish this procedure.