Some important points to note before we start:

Preparatory steps before unlocking your iPhone 3G:

Once your iPhone 3G running iPhone firmware 2.2 (with baseband firmware 02.28.00) is jailbroken, you are ready to unlock iPhone 3G.

Unlock iPhone 3G using yellowsn0w:

1. Launch Cydia from your iPhone 3G's home screen.
2. You need to add the source of the yellowsn0w application. So tap Manage, one of the tabs at the bottom and then tap Sources.


3. Tap the “Edit” button on the top-right corner of the screen.
4. Then tap on the “Add” button on the top-left corner of the screen.
5. You’ll be prompted to add a Cydia/APT URL. Enter http://apt9.yellowsn0w.com/ as the source URL for the yellowsn0w application and then tap the "Add Source" button.
6. Once the source has been added press the "Return to Cydia" button at the bottom of the screen.
7. Then tap the "Done" button at the top-right of the screen. This completes the steps to add the source for the yellowsn0w application so you can install it.
8. Tap on the apt9.yellowsn0w.com source that was just added from the list of sources.
9. Tap on apt9.yellowsn0w.com again from the list of packages.
10. You will get an option to install the yellowsn0w application. Tap the "Install" button on the top-right corner of the screen.
11. Tap the "Confirm" button on the top-right corner of the screen.
12. This will install the yellowsn0w application, you will see the progress on the next screen and the "Return to Cydia" button will come up once installation is complete.
13. Tap on the "Return to Cydia" button and press the "Home" button on your iPhone 3G to go back to the home screen.
14. You need to reboot your iPhone 3G so that the yellowsn0w application which is a small daemon is launched on boot up. Press the “Sleep” button and hold it until you see the “Slide to power off” message. Then slide to switch off the iPhone.
15. Once your iPhone 3G has shutdown, insert the desired SIM card and restart your iPhone 3G.
16. Once your iPhone boots up and you see the “Slide to Unlock” screen, wait for around 10 to 15 seconds (may be more) to see if your iPhone 3G picks up the carrier signal.
17. The Dev team has reported that there is a known issue with SIM cards that have STK (SIM Toolkit) application menus. So if your iPhone 3G doesn't pick up the carrier signal after reboot then try to try to pull out the SIM card and re-insert it, wait for another 10 - 15 seconds and see if your iPhone 3G picks up the signal of the carrier.

If it does then you have successfully unlocked your iPhone 3G.

Some Tips to unlock iPhone 3G if the above procedure does not work:

If the above guide did not unlock your iPhone 3G, then try some of the workarounds mentioned below as it has helped some readers to successfully unlock their iPhone 3G.