Before I begin let me give you a disclaimer:
TETHERING YOUR IPHONE TO A COMPUTER IS AGAINST THE ATT TERMS OF SERVICE
DO NOT DO IT
JAILBREAKING YOUR IPHONE WILL END YOUR IPHONE’S WARRANTY
DO NOT DO IT
Before we get started let me explain some of the risks. Jail-breaking your iPhone can be dangerous, and it voids your warranty. Although I have never personally seen anyone ever brick their phone during Jail-breaking, it has happened. Balance the positives and negatives. Furthermore, using your iPhone as a modem is against your terms of service. In the past ATT has contacted users who have been discovered to have used their iPhone as a modem. Be careful. The “unlimited data plan”, in actually has a 5GB/month limit before ATT will call you to “reassess your needs”. If you do tether your iPhone to your eee PC or other laptop. Be prudent about usage, don’t abuse it, and if you do need a full time mobile modem, tethering is not a replacement, get an AirCard from ATT or Verizon.
With that said. Let’s get to the guide. The process is really quite easy.It essentially involves two steps, 1. Jail-breaking the iPhone and 2. installing the correct software. With that said, let’s get to step one.
Jail-breaking the iPhone:
There are already way too many much better guides on jail-breaking the iPhone out there. So I’m going to be quick and just provide you with the resources you need. You are going to need two things, QuickPwn and a copy of a clean iPhone firmware.
Between the two of these it will allow you to Jailbreak your iPhone in place without losing your settings, and will give you access to Installer.app and Cydia
Once you have Cydia on your iPhone springboard, use it to install PdaNET on your iPhone, and the PdaNET Desktop on your laptop. Furthermore, make sure you have iTunes installed on your eee PC.
Once you have both installed go ahead and restart the iPhone by holding down the power button and sliding it off. This can help with some issues.
Now go ahead and plug the iPhone USB cable into the phone and the laptop, open PdaNET on the iPhone and set it to USB Mode. On the Desktop, right click on the tray icon and click connect. VoilÃ , PdaNET will establish a PPP connection to the iPhone and you’re browsing the 3G network! You can also use WiFi using PdaNET, but I’ve found tethering to be much more reliable, and much easier on both eee PC and iPhone batteries.
I’ve found an interesting way to save on bandwidth and help with speed is to set my Firefox User Agent String to mimic an iPhone. The user agent is how websites know what kind of browser you are using. If you set Firefox to pretend to be an iPhone you will receive web-pages in the iPhone format. Very useful when trying to mitigate bandwidth usage. Here is a guide on how to do it.
Also I recommend that you find WAP versions of your favourite sites. These are websites that have specially formatted mobile versions. Although the 3G connection is plenty fast for most browsing I like to veer on the safe side.
Best of luck!