yeah, this is standard in the syncing, just check off the option in the syncing options, but if you already have a bunch of address book contacts and dont want them to mess up your iphone's contact list you will have to do this:
first, create a new contact group in address book called like "iPhone" or something
second, plug in your iphone and let it sync
third, go to the contacts section on the device listing in itunes, check sync all contacts, then below that, check off add iphone contacts to a specific group (not sure if that's the exact wording), and select the group that you just made
sync again (make sure to do this)
now, go back to the contacts tab and change syncing from all contacts, to only the selected groups, and only select the group you just made, then sync again