Officially it is impossible (as seen by Mr.Jobs short reply: No). Unofficially if you have a jailbroken iPhone (iPhone 2G is not supported), you can use an app called “MyWi”. Simply buy the APP ($9.99). Turn on the WiFi tethering option. Then, all you do is search for available WiFi networks on your iPad, and your iPhone will come up as an available network. It drains the battery, but it still works.