People talk about unlocking iOS4 on iPhone 3G/3Gs and a lot of sites provided instruction already. But I would like to show you how to fix the push notification if it fails after the unlock.
Following are the directions for how to fix your unlocked iPhone.
1, Make sure you’ve jailbroken and unlocked your iPhone 3G/3Gs with iOS 4.
2, Make sure you dont have any app which uses push function on your iPhone. If yes, remove all of them first.
3, Open up Cydia, and add this address to the sources: http://cmdshft.ipwn.me/apt as above
4, Once Cydia is done updating, go to the search field and type in: Push Doctor. Tap it, and then press install.
5, Wait until complete download and install.
6, Restart your iPhone.
7, After restarting, you may install any app which support Push function. e.g. Meebo
8, Run the installed app and it will tell you to enable Push Notification by Tapping Settings.
9, Tap Setting and enable it.
Push Notification should work by now.