Due to the iPhone's lack of MMS support, you can't send pictures from your iPhone directly to Flickr. Even if you tried to e-mail your iPhone pics, they'd be stuck at the 640x480 resolution. Oh well. At least with the iPhlickr app, you can browse through your Flickr account easily. Similar to Flickr's own mobile portal, you can view your own photos and your contacts' photos, plus search for more within a very nice and simple user interface.
iPhone link: http://www.chandlerkent.com/iphlickr/