Hotz says his tool is closer to a "true unlock" and it only patches three files to do so. He also notes that it addresses the Wi-Fi and battery issues seen with the Dev Team's unlock called "ultrasn0w." If you're skeptical about his claims (and a developer), you can look at the purplesn0w source code and decide for yourself if his work is better.

Unlocking vs Jailbreaking

In case you're unfamiliar, jailbreaking and unlocking are two entirely different things. Jailbreaking is simply a type of hack that lets you install unapproved third-party applications on your iPhone or iPod Touch from searchable repositories provided by apps like Cydia and Icy. Unlocking, on the other hand, is a hack that lets you use your iPhone on another cellular network. Here in the U.S., that means you can use the iPhone on T-Mobile instead of AT&T. You have to first jailbreak your phone before you can unlock it, but you don't have to unlock a phone in order to jailbreak it.

How to Unlock Your iPhone 3GS in 4 Steps

In order to unlock your iPhone 3GS to work on another carrier's network, you have to first jailbreak your phone. The instructions below assume you have already done so. Because jailbreaking is a more involved process, we won't document it in this post. (Note: you can read our online guide "how to jailbreak your iPhone to OS 3.0" to jailbreak your phone).

In this case you'll want to use the software "purplera1n" to perform the jailbreak before using purplesn0w.

As always, it's a good idea to have a current iPhone backup in place in case something goes horribly, horribly wrong and you have to restore your device to factory settings.

Also note that at the present time, your phone will have to already be activated in order for this unlock to work. However, it sounds like a "hacktivation" is in the works -meaning that, in the future, you won't need to officially activate your phone with AT&T (or your country's default carrier) first.

1. Disable 3G: Go into "Settings," "General," "Network," and then tap the slider that reads "Enable 3G" to set it to the OFF position. Exit back to the main screen when finished.
2. Add the Geohot Repository to Cydia: Again, since you've already jailbroken your phone, you should have the Cydia app on your iPhone's screen. Launch the app and select "Manage" from the set of buttons at the bottom of the screen. Tap "Sources," "Edit," then "Add." Type in apt.geohot.com and hit "Add Source" when done. Tap the "done" button and exit out of the "Manage" section.
3. Install Purplesn0w: Do a search for "Purplesn0w" using Cydia's search utility. (Actually, since Cydia updates results as you type, you really only need to enter the first few letters.) You're looking for the package com.geohot.purplesn0w. Once you've found that, tap it to see the details. Next, tap the "Install" button and then the "Confirm" button just as if you were installing any other Cydia app. Wait while it installs and watch for the success message output in Cydia. Tap "Return to Cydia" when it's finished installing and then exit from the Cydia app entirely.
4. Reboot Your iPhone: Press the power button (at the top of the device) until you see the message "slide to power off" appear. Use the slider to power off your device then turn it back on. Once rebooted, your iPhone 3GS will be unlocked.

Note: You can follow the same steps as above to install the ultrasn0w unlock as well, if that's your preference. The only difference is that the repository to add to Cydia is http://repo666.ultrasn0w.com and, obviously, you'll be looking for the ultrasn0w app to install.