Is it possible to jailbreak an iPhone 3GS that isn't made after particular baseband on 6.0.1?

Hi, I've lost my 4S so I'm going back to my 3GS til I get a replacement. Unfortunately, since I upgraded my phone, I've also switched carrier so I need to unlock my 3GS. The carrier I was on is asking for a fee to unlock (cos they're dodgy like that), so I tried to jailbreak with RedSn0w then unlock with UltraSn0w. I upgraded to iOS 6.0.1 then tried to jailbreak. All the prompts ran through successfully with RedSn0w but Cydia does not appear. Jailbreak unsuccessful? Anyway, I read up a bit burther and saw that if your 3GS was manufactured after a particular date, you can not use the iPad baseband (which is what I was about to try) since it'll brick your radio, hence effectively turning your iPhone into an iTouch... Is there a method of doing this on iOS 6.0.1 for a 3GS made after that particular date or will I need to downgrade to another iOS (I don't mind downgrading to 5.xx since my 4S was still on that anyway)? I did look into downgrading as well, but couldn't get it working. Had issues with verifying blobs or something? I have no idea what that means. Anyway, much appreciated if I can get some advice on how to fix the jailbreak to unlock on iOS 6.0.1 or downgrading to iOS 5.xx to unlock. Thanks, B