Got Jailbreak? Don't Care About TOS? Get iPhone 3G Tethering!
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).
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...