My notes, things I have learned, and documentation I have created.

I suppose the first question is why downgrade the baseband now? Well, I got AT&T to unlock my 06.15.00 baseband 3Gs when it was announced that they would if you phone was no longer under contract. The only reason anybody installed the iPad (06.15.00) baseband was to unlock their phone. Since, it was no longer needed I wanted to be able to update my phone without having to use redsn0w to install a custom ISPW each time.

Software used:
Redsn0w 0.9.14b1.zip
iPhone2,1_5.1_9B176_Restore.ipsw

Download redsn0w 0.9.14b1.
Unzip redsn0w.
Download the version of IOS currently running on your device. 5.1 in my case.
Launch redsn0w.
Select Extras.
Click Select ISPW..
Navigate to the downloaded ISPW for your version.
Click Back.
Select Jailbreak.

If already jailbroken, uncheck Install Cydia and select Downgrade from iPad baseband.

Ensure that the phone is connected to your computer, and put it in DFU mode or hit Next and follow the prompts on the next screen. It might take you a few times to get the timing right.

Redsn0w will begin fetching baseband files.

The phone will reboot and you will get a message in redsn0w stating that the rest of the process takes place on your device.

On your phone, you will see several message on your phone relating to disk checks and then the familiar running pineapple on screen. Be patient.

Your phone will reboot with the downgraded baseband.

Now, if you want to go back to a completely stock installation, you will need to restore the most currently supported version of IOS (5.1.1 for the 3Gs), after putting the phone back into DFU mode.

Got my iPhone4 on Wednesday (6/23/2010), so I spent the previous weekend jailbreaking and unlocking my 3Gs. Unfortunately, I used Spirit to jailbreak my 3.1.3 iPhone3Gs with the 05.21.01 baseband and it was the first time I did jailbreak the phone. So I was unable to update it to IOS4. I need it be unlocked to work on Tmobile. Nonetheless, using it was better than I thought it would be, but the signal in my home is really weak unless I am upstairs. I am keeping an eye out to figure out how I can update it to IOS4 and unlock it.

By the way, I like the new phone a lot. I had issues getting it ordered, but I only did it through Apple. And I have to say to everybody that was complaining about AT&T, Apple had their own issues too. A lot of the time was when it was verifying my AT&T account, but there were other times when it was all Apple. I was able to get my order processed at about 5pm Pacific time.

My only issues so far have been the sharp edges. I hate having to use a case, but I think I going to have to. Also, I have noticed the signal degredation, when holding the phone in my left hand, which I do all the time. The case should help with that too.