iPhone 2.0 Upgrade Steps for 2G iPhones ACCIDENTALLY Upgraded to 2.0 already.
Follow and check all steps and all will work.
=== Pre-upgrade Checks ===
1. Restore your iPhone with the Original & Official Apple iphone 2.0 software.
2. Phone will be "emergency" only status.
=== Device Support Folder === (2.0.1 should solve this but check it anyway

)
1. Open Finder
2. Goto "Mac HD"
3. Goto "Library" and then to "Itunes"
4. If "Device Support" EXISTS - open folder and delete everything in there.
5. If "Device Support" folder doesn't exist - create a new folder called "Device Support"
=== Download Bootloaders ===
1. You need both 3.9 and 4.6 (available via 100s of links on this page - particularly at the top)
=== Upgrade Steps ===
1. Open up the pwned 2.0
2. Goto EXPERT MODE - if you use simple mode you will get errors 6, 20, 1600, 1601 etc and it will NOT work
3. Select the 2.0 firmware and also select relevant *.bins
4. When get to main menu screen, go into Bootnetuer and select "Update Bootloader" and select "4.6"
5. Go back to main menu and enter General Settings --> select Enable Baseband Update
6. Then build the firmware and save it to your desktop
7. Once the firmware is built, pwned will ask you to plug in your iphone via USB.
8. It will then step you through the process of enter DFU mode
9. Once this is complete it will ask you to boot up itunes (when you plugged you phone in it may have already loaded)
10. Hold down ALT (on MAC) and select the firmware on your desktop
11. iPhone will update - LEAVE IT for the entire process.
12. It should install and all will work
=== If DFU Fails ===
1. Plug iPhone into USB & then TURN OFF (connected obviously

)
2. Hold the power and home buttons at the same time for 10 secs
3. Release power button and continue holding home button
4. iTunes will recognize the phone in "Restore Mode"
5. Hit "Option/ALT" key and click restore.
6. Select the firmware on your desktop
7. Await 2.0 love (feel free to drink a beer at this point)