According to the iPhone demo activation video you cannot sync Outlook Tasks to the iPhone.
Only Media, Calander items, Contacts, and notes.
I guess you can actually schedule meetings and talk with people while trying to organize your life around your new phone. But never actually GTD by checking off and creating task lists and categories. This could be exactly why it is not considered a business phone.
Someone please update me on this ans say it ain't so.
02/22/2008 update.
Well according to this blog entry at TUAW apparently something is in the works with some upcoming iCal task support on the iPhone.
I still smell something fishy though and feel that it is still odd that it doesn't exist.
03/11/08 update.
I have since heard of the Nozbe service from the Slashdot Review Podcast.
I will check into this and see if it solves the tasks on the iPhone issue. It looks like it may be one possible solution.

04/08/08
Well now that I have my new iTouch that I got for my 30th birthday I am still looking for a task application that will work on the iPhone without requiring Wifi access.
I just found this site: Toodledo Comparison which looks like it is better that Nozbe and can even import csv files from Outlook. YEAH! I will keep you posted with what I find out.