How to Unlock Your iPhone

 If you're one of the million people who've purchased an iPhone since the end of June, you probably signed up with Apple's exclusive carrier in the U.S., AT&T, when you activated your phone. That means your iPhone identifies itself to AT&T's network using an AT&T SIM card, a smart card that's located in a small tray between your iPhone's sleep/wake button and its recessed headphone jack.

 But what if you're planning a trip to Europe and rather than paying AT&T to use the networks of its European partners, you want to take advantage of the favorable rates and local phone numbers offered by replacing your AT&T SIM card with a pre-paid European card? Or what if you'd prefer to use T-Mobile as your cellular provider, rather than AT&T?

In the past month several groups have announced that they've found a way to "unlock" the iPhone, allowing it to use a SIM card from any provider. (Keep in mind that this is only half the story: the iPhone uses the GSM radio band for its communications, meaning that it'll only work with providers that use the GSM network. In the U.S., that means T-Mobile and AT&T.)

In August, a group of hackers demonstrated a method for unlocking SIM cards and sold its software to resellers, who in turn began selling it to the public for as much as $100 last week.

But another group has came up with its own hack that, with the help of some free, open-source software, lets you unlock your iPhone in about an hour, free of charge. Below, I'll show you how it works - and it does work, because I've used this technique to unlock my own phone. (One important caveat: Certain AT&T-only features, such as Visual Voicemail, will not work when you're connected to other cellular networks.)

Before we get started, you'll want to disable the iTunes helper application that may get in the way of the installation. Make sure iTunes is not running, then open OS X's Activity Monitor in the Utilities folder of the Applications folder. Search for or scroll down to iTunes Helper, select it, and then click on the Quit Process button in the top left of the screen. You'll also need your iPhone, your data cable, and a Wi-Fi connection to the Internet.

(If you haven't already activated your iPhone with AT&T-and aren't planning to-you need to conduct a fake activation. To do this, you'll need to follow the excellent instructions at ModMyiPhone and download and install a program called iNdependence.)

Install AppTapp

Apple doesn't support the installation of third-party applications on the iPhone, but the enterprising developers at NullRiver have created a program called AppTapp that will let you install including chat clients, games, and other pieces of software - including those that are needed to unlock your iPhone.