Step1 If you are on 3gs 4.1 just download 4.1 ipsw from below links. If you have already 3gs ios 4.1 than skip this step
2 : Run Redsn0w 0.9.6b5 select 4.1 ipsw wait for load up
3: Tick install cydia and install ipad baseband in Redsn0w app
4: Follow instructions in Redsn0w apps to proceed. it takes 2-3 minutes to fetch baseband from net and upgrading to your phone.
5. Wait for phone to power on
6: Connect wifi Run cydia and let cydia finish database update
7: Go to manage/sources and install ultrasn0w
8: Restart phone and voila! you have an unlock iphone 3gs 4.1 with baseband 6.15
3GS ios 4.1 Download
Redsn0w 0.9.6b5 for Windows Download
Redsn0w 0.9.6b5 for Mac Download
Note: This procedure will update your baseband to 6.15 and it will void warranty. You will not be able to Downgrade baseband.
