Jailbreaking a locked iPhone 4s with iOS 6
As of January 2013, there is no jailbreak for iOS 6. The reason is that iOS 6 introduced new security mechanisms and fixed the exploits that made the jailbreak possible on iOS 5.

You will have to wait.

Recent articles (December 2012):


Pod2g breaks silence on iOS 6 untethered jailbreak » Phone Reviews
Hacker: jailbreaking iOS 6 hard, 6.1 may prove impossible | iPodNN


Other good and curated jailbreaking news can be had at:


http://www.reddit.com/r/jailbreak (especially this thread on 6.x jailbreaking)
https://twitter.com/planetbeing
https://twitter.com/chpwn