Following guide can help you to activate iPhone 3GS, and iPhone 3G jailbroken with Redsn0w 0.9.6b5 or PwnageTool 4.1.3 and Ultrasn0w 1.2 unlocked, to fix battery drain with Redsn0w 0.9.6b6.

How to Activate iPhone 3GS, 3G to Fix Battery Drain with Redsn0w 0.9.6b6

Step 1

Download Redsn0w 0.9.6b6 for Windows or Mac
Download iOS 4.2.1
Download iOS 4.1

Step 2

Jailbreak your iPhone by using following guides

Jailbreak iPhone 3GS, 3G iOS 4.2.1/4.1 with RedSn0w 0.9.6b5
Jailbreak iPhone 3GS, 3G iOS 4.2.1/4.1 with PwnageTool 4.1.3

Step 3

Open Cydia on your iPhone and add this repo http://repo.bingner.com

Step 4

Go to added repo and install SAM and SAMPrefs packages available there

Step 5

Now, attach your iPhone to your system and run Redsn0w 0.9.6b6

Step 6

Browse iOS 4.2.1 or iOS 4.1

Step 7

Check mark the box followed by Deactivate and go Next, then follow the on screen instructions to complete RedSn0w process

Step 8

When your iPhone will reboot, open Settings > SAM and enable De-Activate iPhone

Step 9

Then connect to iTunes and

If iTunes says invalid SIM, you will need to manually select the appropriate carrier, under one of the methods besides Automatic and click on a SIMID

If you installed SAM and manually set your carrier but it is not working, please be sure you clicked on the SIM ID even if there is only one

Unlock iPhone

Now you can unlock your iPhone with UltraSn0w 1.2, see How to Unlock iPhone 3GS, 3G with UltraSn0w 1.2