Apple & AT&T have confirmed that 3G tethering will soon be available on your iPhone. Users will soon be allowed to connect wireless to their laptops, computers, and other mobile devices.
Tethering has already been available to users who jailbreak their iPhone, with an open SSH connection. Jailbreaking allows users to access files not available any other way on their device. This has allowed communities of customization to the iPhone be relatively available to anyone who Jailbreaks their device.
The functionality and release date have not be confirmed as of yet, but many suspect an announcement coming soon from Apple. Speculations about whether this will be free or not has not been confirmed from Apple.