Iphone3gs jailbreak without a sim card?

Okay. So my mum's friend gave me his old iPhone.
iPhone3Gs. Without the sim.
Basically, I don't even know what's happened, but I've basically updated it to io6, and I can't Jailbreak it now. I just need someone to tell me how to change the firmware back to 5.1.1 so that I can Jailbreak it. Is the best way uninstalling itunes or? FML. Arrrggh.someone help please

You don't need to downgrade. Just follow te steps on this page.http://www.gottabemobile.com/2012/09/20/how-to-jailbreak-ios-6-for-iphone-4-iphone-3gs-and-ipod-touch/

Cellphone

o p e n ; link n°2&3