I have an iPhone 3G, and made the mistake of upgrading to iOS4. It has progressively gotten worse in the months since I upgraded to iOS4, and now it is frequently unusable. I want to downgrade back to iOS3. If I do a backup of the phone right now, and then downgrade to iOS3, can I restore all the app data, contacts, voicemails, call logs, phone settings, etc. back onto the phone?