According to Jobs: No iPhone-to-iPad Tethering, 10 Hour Battery Life Reaffirmed
Swedish site Slashat.se reportedly emailed Steve Jobs asking the simple question "Will the wifi-only version somehow support tethering thru my iPhone?" Steve Jobs' reply was a simple "no" and was sent from his iPhone.
Tethering is the process by which you can share an internet connection from a cellular device (such as the iPhone) to a non cellular device such as a notebook, or in this case an iPad. If tethering were allowed, the iPad could share the iPhone's 3G connection removing the need for purchasing wireless service on the iPad itself. The answer is not a surprise as Apple had given no indication that the iPad could service this function.
Meanwhile, Jobs has been busy answering emails as he had also responded to disbelief that the iPad's IPS display could support 10 hours of battery life in such a small form factor. To these inquiries, Jobs replied:
"... yes, we are getting 10 hours in 1.5 pounds."
Notably, in this email, he actually responded using the iPad.
The iPad launches in the U.S. on April 3rd with pre-orders starting on March 12th.