This seems to work according to Hackintosh.org.

(http://hackint0sh.org/forum/showthread.php?t=1342)

-Sign up with AT&T

-Wait until you get the email that activates your iPhone

-Call AT&T and cancel your contract. You have 30 days to cancel. The iPhone stays activated.

Now you can use nearly all of the features of the iPhone without paying AT&T a monthly fee, or having to cancel a cell phone contract with another carrier. It is so slim and compact, it won't be a problem to carry your regular phone and your new (M)iPhone.

And it won't be long before people figure out how to install a VOIP widget to use when you are in a WiFi spot.

Please see: The Trojan Horse iPhone: How Apple will Break the Back of the Wireless Telco Cartel and Trigger Silicon Valley's Next Boom Cycle