Another tip for you iphone owners who have broken out of jail (Jailbroken), and want to tether your iPhone for free. Follow these simple steps and you are on your way to using your laptop and iPhone together to tether, without the intervention of your mobile carrier.
On your iPhone:
1) On your iPhone, locate and access Cyndia, the jailbroken installer and search for an app called PDANet, and install it.
2) Once you have it installed and its available on your Springboard, access it and choose between the options of USB or WIFI. It’s up to you, but if you use Wifi you have to set up a wifi ad-hoc network (on your mac you can do that easily by going to network menu icon and creating a new wifi location). Once you have that set, find the wifi spot on your iphone and then access PDANet and you should be able to see a dashboard stating that you are connected and ready to access the net.
On your Mac/PC:
Well, if you decide to not use Wifi and instead opt for USB, you need to download the desktop client and install it. It will ask you to reboot and after you return back, you have a taskbar/menu icon that allows you to connect to your wifi (provided you hooked up your phone to your computer).
Hope this helps. You can use this technique with Android as well as Windows-based phones, so not exclusive to the iPhone, but definitely a worthy project these guys have been working on!