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):