How I learned to Unlock my Cell Phone - my iPhone 3GS
At one time, when I was asking around trying to unlock my cell phone, I found out that I should probably word it better when I say that. There is a difference between unlocking iPhones, and jail breaking them. They are two completely different hacks, that give you control over your iPhone in completely different ways. Unlocking, the more popular of these two terms, is the trickery that will let you buy your iPhone from AT&T, and hack into its protective features that keep other networks, like T-Mobiles out. Jail breaking is a hack that will let you use third-party apps on your iPhone, ones Apple doesn't approve of. And this is something you'll need to learn to do, as one of the steps on your way to learning to unlock your iPhone.
Now the iPhone 3GS has been impregnable until was recently. Usually, it is a group of self-styled experts that does all the pathbreaking unlocking and jail breaking on the iPhone - called the Apple Dev Team. With the iPhone 3GS however, a motivated dude named George Hotz beat the Dev Team to the line - with purplesn0w, the latest unlocking tool I found to unlock my cell phone with. The most impressive quality purplesn0w has to recommend it though is that it does its deed with the minimum carnage possible. It only alters three of the iPhone's original files to get the job done.
I found out how to unlock my cell phone, well, my iPhone 3GS anyway, in just a couple of steps. Let's assume that you have the jailbreaking process out of the way (using the purplera1n jailbreaking code), and just concentrate on the unlocking process at this time. Before you start with the actual unlocking, make sure you backup iPhone's contents, because you can never really tell what happens with these risky procedures. If things go awry, we'll need to reset your phone, an action that would certainly return your phone to the way it was out of the box - no content or numbers at all.
Make sure that your iPhone is properly activated on your real provider first. And then, on the iPhone, you open Settings, then General and finally Network. When you jailbreak your phone with the right software (with purplera1n), it installs on your phone, a strange sounding piece of work called Cydia. You'll need to use it now. Turn it on, pick the Manage setting. Follow the route Sources - Edit - Add, and then key in a string of nonsense called apt.geohot.purplesn0w. You follow up that beauty with a tap on the Add Source button and the Done button, and, you're done. I thought that I was good to go with this, but I found out that to unlock my cell phone required one more step and a reboot.
That's kind of an important step - installing Purplesn0w. You'll need to search for the package com.geohot.purplesn0w on Cydia on your phone, then install it. Once you're done, you reboot, and there you go. This is how I've learned to unlock my cell phone. Hopefully, this will work for you too, for a good long time.