Tether iphone to computer and use the GPRS on iphone to get on the Internet.
Things you need.
1.Jail broken iphone
2.Unlimited GPRS account even regular ones work but unlimited is preferred.
3.A computer with wifi connection.
The iphone and the computer should have same Wifi standards. My laptop was wifi g.
If you have all the things mentioned above then go to cydia installer on your iphone and install a app called pdanet. One you install the app.
Go to your computer and create a ad hoc wifi connection by going into connect to option in vista or network settings on Xp.
Once you create the wifi ad hoc connection. Go to your iphone and turn on wifi and you should see the connection you just made. Select the connection to connect. Once it's connected open the pdanet app and just turn on the wifi switch at the bottom. And start using Internet on your computer, this app show the computer name Mac address and the transfer speeds.
Just turn of the display by clicking the power button on your iphone and enjoy the internet.
It's as easy as that.
One more thing don't use this for hours on end because the iphone can get hot pretty quickly. So keep checking the iphone by touching the iphone. If it's really hot disconnect it and use it after a while.
I tried it with vista and Airtel sim. Airtel needs no settings just put the sim in the iphone and GPRS works, which is cool. It even works on my 2g or first gen iphone.