Can I Jailbreak my iPhone on 3.1.2?

How to Activate my iPhone 3GS wtih AT&T Sim and Jailbreak?

• Hi a few weeks ago I upgraded my iOS through iTunes for iPhone 3GS 8GB from 4.1 (Jailbroken & Unlocked) to 5.0.1 (Baseband 6.15.00), and then jailbreaking it with redsn0w + cydia -> as result - ultrasn0w unlock didn't work and my mobile provider was not descovered. I have an iPhone 3GS with the last three numbers of the first 5 numbers higher than 135, so i have an iPhone 3GS made after the 28th week in 2011 and also it's a new boot rom. I've looked at many solutions, but my last solution appears to be flashing my baseband to the iPad's but my iPhone 3GS is not supported from that confirmed by this video (How To Unlock iPhone 3Gs 5.0.1 for Tmobile & Fix No Service Error - 5.16.05 to 6.15.00 - Ultrasn0w - YouTube). I tried restoring, and jailbreaking it again, and still I receive the 'No Service' message. I am aware that flashing to the iPad baseband means i can no longer get a stock IPSW or downgrade. So now i'm currently on 4.1 Jailbroken but with 'No service', So I decided i'm going to purchase an AT&T Sim card from Amazon. So I see that everyone goes to ultrasn0w to unlock their iPhone's to any carrier, i had this luxury as well, I want to know, if i buy a never activated, AT&T Sim card and restore my iPhone 3GS on 4.1 and activate it with that, will i be able to then switch it/swap it out with my carrier here in The Bahamas' SIM card or any carrier for that matter? What is the process of doing this and also having a 4.1 jailbreak as well? Thanks in advance.

• Answer:

  http://idailyreview.com/how-to-downgrade-your-a4-idevice-from-5-1-to-5-0-1/