Go to jailbreakme.com for info like this. They have a nice page telling you which versions can be jailbroken and which tools to use. If you visit it with your iPhone, it even detects which version you're using and tells you if you can jailbreak and how you can jailbreak if you can.
Right now, there is no jailbreak (tethered or untethered) for the iPhone 4S running iOS 6.x. Looks like the iPhone 4 has an advantage