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.

A couple things I discovered when attempting to remove the jailbreak from my iPhone 4s:

1) You cannot just delete the Cydia icon. When you press down on the icon and all the icons start wiggling, you have no option to press the “x” to delete the icon.

2) If you try to reset the phone by going to Settings/General/Erase All Content and Setting, this process will either never start or never finish. You end having to hold Power+Home to restart the phone.

So I tried to restore the phone. I was running 5.0.1 and wanted to keep it that way. Now, the simplest way to do it would have been to put the phone in DFU mode and download and restore the latest version of IOS from Apple. However, as I stated I wanted to try to keep the same version of IOS, 5.0.1 in my case. I downloaded the latest version of redsn0w , unzipped it and ran it. With the phone in DFU mode, I chose Extras/Even More/Identify. This verified that my phone was in DFU mode. Next, I went into Extras/Even More/Restore, and clicked ISPW and browsed to the version of IOS I wanted to restore. At this point, you are prompted to browse to the most current version of IOS (5.1.1 in my case). This is required to upgrade the baseband. If you do NOT want upgrade the baseband, DO NOT DO THIS! Once the latest version of IOS has been identified, you need to tell redsn0w where to find your shsh blobs. I chose remote to pull them from the Cydia servers, Once that is done, click Next and the baseband is upgraded and IOS 5.0.1 is restored. If you want to preserve your baseband, then you need to go the Extras/Custom IPSW route.