After some Googling, found this link which seems to work for many: http://www.blogsdna.com/5468/how-to-unlock-iphone-3g3gs-3-1-2-os-using-blacksn0w.htm
My phone wasn't jailbroken before, so the first thing I did, according to the website was to download the Blackra1n software here: http://www.blogsdna.com/5465/download-blackra1n-rc3-to-jailbreak-unlock-iphone-3g3gs-3-1-2.htm
Now this application looks pretty shady - just one button in the interface:
WTF!Anyway, went ahead and clicked on the make it ra1n button. Following are the screen shots of what happened next:
As soon as this was over, iTunes popped up a message saying:
I for a second thought this was a message from the Blackra1n and I went ahead to do the restore. I think this was unnecessary. What I actually should have done is to disable the iTunes helper from the background processes. This was what I found after doing some more reading on the net! Anyway, my iTunes is restoring my iPhone now. Waiting for it to get back! Once done, I restored the phone to the latest backup which I had done before going ahead with this unlocking act of mine!
Repeated the Blackra1n again.. Now my iPhone is restarting as mentioned in the website. After the restart, you'll find that there's an App in the phone called blackra1n. Open it, and there are three packages as shown below:
Check all of them, and tap install on the top right. iPhone will now download the packages and install them.
If everything goes fine, I'm just one step away from unlocking my phone - restart! Hope it works!
Now installed packages, but it got stuck at "Unpacking Sn0w". No idea why. So I exit the app. Opened it again, and installed Sn0w again. This time, it downloaded, installed and gave me a message saying iPhone is unlocked and comm services restarted. No need to reboot.
It was only now that I removed my AT&T sim and inserted my AIRCEL local sim. It took a while to acquire network, but it worked! Restarted my phone just to confirm - Aircel it is, and I'm able to make calls! Yoyo!!
And by the way, the blackra1n app installs Cydia - an appstore for thirdy party applications, and Rock - haven't quite figured out what that is!
Now testing other functionalities -
Wifi - Oops doesn't work! No problem, just reset network settings from Settings - General - Reset. Once this is done, it works fine!
Safari - Works
Mail - Works
Facebook - Works
Cydia - Works
Rock - Works
Phone - Works
SMS - Works
iTunes Syncing - Works
All other apps - Work as they are supposed to.
Speed - No difference from how it was previously. But now, I have an entire range of third party (some even cooler than what's available on App Store) to try out from.
Restarted phone. Connects back fine to Aircel as well as my Wifi network. So far so good! Kudos to Blackra1n and the developer! Good job George Hotz!
Summarizing steps for a perfect unlock:
1. Back up and Restore your phone to OS 3.1.2.
2. Once you've restored you phone, you're done with iTunes. So exit the program. Force Quit (Mac) or End Process (Windows) the iTunes Helper process.
3. Download and run the Blackra1n RC3 from the above mentioned link. I suggest you also go through the website for a better understanding of the Backra1n "features".
4. Let Blackra1n do its job, and wait for the iPhone to restart.
5. Locate and run the Blackra1n app, and install all the three packages.
6. Insert your new sim, and enjoy!
I've mentioned some of the problem I faced while unlocking; so if you happen to face similar issues, you know what to do!
