Depending on your carrier, their terms of service (TOS), and your willingness to break said terms and face possible consequences including death-by-over-billing, you can now tether you newly pwned/jailbroken iPhone 3G to your laptop to share the mobile 3G internet connection anywhere and everywhere you go (your coverage area, of course, may vary).

The process is a little involved, according to Macrumors (via Cre.ations.net):

Jailbreak your iPhone 3G. Install 3Proxy and Terminal. Create an ad-hoc Wi-fi network using your laptop. Join the network with your iPhone. Find the iPhone's IP address Open Terminal and run the proxy program. Open Safari on your iPhone and open a web page. Configure your browser to use the proxy.

Not a 133t level hax0r? Don't worry. AT&T (and other carriers) might just offer this option, complete with inevitable bandwidth cap, 'natch, sometime in the next millennium...