Jailbreaking your iPhone - iPhone 3.1.3

So you upgraded your new-ish Apple iPhone 3GS to software version 3.1.3, and you lost your jailbreak? There's a way to get it back as long as you meet certain criteria:

• the version of the iPhone doesn't matter eg: could be a recent MC version;
• you have previously jailbroken it and you used Cydia; and
• when you used Cydia you clicked the "Make my life easier, thanks!" link

ToolJail 1.3.2 by Destructor95 will walk you through the steps to downgrade to 3.1.2, by using:

• Sn0wbreeze 1.5.2. by iH8sn0w (this helps you downgrade to 3.1.2); and
• BlackRa1n by Geohot (which does the jailbreak)

ToolJail will help you download the files you need.

This is by far the simplest explanation I have seen on the Internet. Plenty of sites try to describe how to do it, but many such as redmondpie.com are a bit circular and are not very clear. However, thanks to redmondpie.com for bringing ToolJail to my attention!