Hi all. Just wanna share my experience. For me, the best tethering apps out there (on jailbreak iphone of course) is PdaNet. It's free for 30 days and u can use ur iphone 3g broadband internet to share with ur laptop.

How to install:
1. Open Cydia, search for PdaNet and hit install.
2. Open PdaNet website http://www.junefabrics.com/desktop/ and install the desktop client.
3. Open PdaNet on ur iPhone, click settings and set PdaNet to connect tru USB cable.
4. Open PdaNet client on ur laptop and click connect.
4. Done! Enjoy ur 3G connection from ur laptop.

*This applies for Windows (XP or Vista x86 and x64)
*U can also use wifi connection if u forgot to bring ur usb cable

I just don't hv time to explain in detail. But if u can use iPhone, meaning that u are somewhat tech savvy and I believe u can sort this out. Just one thing to keep in mind, iPhone OS3.0 support tethering by default (find that in the Settings>Network) and u dont really need any 3rd party software. BUT u may be charged again for tethering usage even though u already subscribed for unlimited 3G (dont know if this really true?). Cheers!

-abejoe-

Coz the official tethering doesn't work for me. Once I pushed the button to "On" suddenly it disappeared. I wonder where it's gone? Secondly, as I said before, u may be charged again for using tethering even if u already subscribed to unlimited 3G.