Okay so I have an unlocked iPhone on 3.1.2 but I want to upgrade it to the new iOS 4 and then unlocked that. I have steps to unlock the iOS 4 but what steps do I need to take to get rid of the 3.1.2 and upgrade?
If you update your iPhone 3g, two possibilities may happen ;
1. If you have a jail broken iPhone, You will lose your jailbreak
2. If you have an unlocked iPhone, you may lost it too.
Before updating your iPhone , you need to take backup of your data files from your iPhone . After that, use Remote unlocking method to unlock it . It doesn't requires jailbreaking and it is one of the permanent unlocking solution too. After unlocking your iPhone using this method, you can update or downgrade your iphone without any interruption . it won't gets locked again . If you have completed unlocking and updating process, you can use restore service to restore your data files from backup .
Source ;
Unlock-zone.com