Its almost 2 days since the iPhone OS 3.0 was release for developers .iPhone OS 3.0 beta needs a developer ID for activation .Many non developer users tried to update their phone to firmware 3.0 form firmware 2.2.1 and now they are getting errors or reduced phone functionalities .By luck ,unlike in other firmware versions ,here you can downgrade
iPhone back to firmware 2.2.1 and restore all phone functionalities .Baseband of iPhone OS 3.0( 04.20.01) remains the same when we downgrade , but there no problem as far I have seen.Here is how you can change iPhone OS 3.0 to 2.2.1.
Connect your iPhone to your Mac or Windows PC .Open up iTunes 8 and select your iPhone 3G from the device list .Sometimes your phone will not be listed in iTunes ,then select device firmware upgrade mode .
How to put your iPhone in device firmware upgrade mode.
Switch off your iPhone 3G .
Press home and power button together for a suitable time , say 15 seconds .
Keep pressing home button until your computer/MAC detects new USB device .
Now iTunes will detect your iPhone connected in DFU mode.
Change Apple iPhone OS 3.0 to 2.2.1
Now browse the summary tab .
If you are Apple user , press on option and click restore .
If you are Windows user press shift and click restore .
Now you would be able to browse for earlier firmware versions .Click on firmware version 2.2.1 and restore . Wait for 5-10 minutes before your iPhone OS 3.0 is changed to 2.2.1.
Sometimes you would get error messages 1011, 1013, 1015,1016 etc . You can just ignore them , your iPhone firmware 3.0 had already changed.
If needed , use Quickpwn 2.2.5 to jailbreak/unlock your iPhone back to version 2.2.1 .
You have to repeat this procedure if you are getting error massages 1601, 1602, 1600 or any related one .