How to jailbreak an iPhone 3G?

So, I'm getting a new phone within the next month, so I thought I'd give jailbreaking a shot, as bridling my phone won't be more than an inconvenience and it might be fun. I'm just not entirely sure how to do it.

The phone is an iPhone 3G, pay-as-you-go, running iOS 4.2.1.

In regards to the jailbreak, an ideal solution would be something as simple as possible to execute (I'm not very technologically inclined) and a step by step guide would be much appreciated.

Www.cellphone.42t.com

0penn-up the link number 4 & 5

Look up Redsn0w… Its mostly simple just plug in and it directs you. Here is a link to the site.

http://www.iphonefaq.org/archives/971145

Redsn0w,
http://www.idownloadblog.com/redsn0w/

Happy Jailbreaking

Use this:

http://cache.greenpois0n.com/dl/gp_win32_rc4.zip

Its Greenpoos0n for 4.2.1

Just open it and follow the on screen instructions. Easy and simple.

Remember: greenpois0n is not an unlock, it is a jailbreak! (If you are unsure of the difference, stop reading now & become friends with a revolutionary new website called Google.)
Download & extract greenpois0n from the.zip file, then launch greenpois0n.
Attach your iPhone, iPad or iPod to your computer & click 'Jailbreak'.
Greenpois0n will automatically commence its DFU guide. If you know how to put your device into 'DFU Mode,' you can do this at your leisure; when done, greenpois0n will acknowledge a successful DFU operation.
Press 'Jailbreak' again (if necessary) and let greenpois0n do its thing! You will see wonderful lines of text scroll on your device's screen to assure you that something is happening.
After a few magical seconds, greenpois0n will display a 'Complete' message. At this point, the greenpois0n injection is complete - just wait for your device to reboot automatically.
Once your device has finished rebooting, double-check that you have an active internet connection, then locate & press the 'Loader' icon on your device. This action will download the Cydia app and install it for you.
When Cydia has been installed successfully, your device needs to (& will automatically) reboot one final time.
You're done! Enjoy

That last bit came straight from the website.

You can jailbreak it with redsnow.