The most popular jailbreak app to enable tethering on the iPhone is MyWi, which costs $19.99 while iPhoneModem costs $9.99 and PDANet costs $29.99.
The process of tethering allows your laptop to use your iPhone's data connection to surf the internet.
Here is a brief description of TetherMe:
TetherMe dynamically enables native tethering for iOS 3.x and iOS 4.x+ devices. This should work on any carrier without the need for customized bundles or preferences.
TetherMe also bypasses signature checking and allows you to edit your carrier bundle manually if you so desire. This is required to enable MMS functionality on T-Mobile. TetherMe does not enable the loading of APN configuration from .mobileconfig profiles at this time.
TetherMe is available on Cydia for $1.99. Once you have purchased and installed the app, reboot your iPhone and then navigate to Settings –> General –> Network to enable or disable it.
As always, let us know how it goes.