Facebook announced a version for the iPhone. The formatting and content of the site is rearranged to create a more pleasing iPhone experience. I just logged on from my iPhone and found it far superior to navigating the tradition Facebook site from the iPhone.
Of course, there's not really an "iPhone version" since the iPhone version will work on anything with a browser. It's not as nice on a full sized browser as the traditional formatting, but it would probably be nicer on, say, Opera on your Razr (someone let me know, please).
Earlier, Netvibes introduced an iPhone version of it's site as well. Looking for an RSS reader for the iPhone, Netvibes might do the trick. I'd like to know what you think of it.
This brings up an interesting point. The iPhone isn't likely to become a dominant player in the HUGE cell phone market, but I do believe that it will create significant pressure on other cell manufacturers to smarten up their smart-phone offerings. One of the key things there is a larger screen.
As more phones with larger screens become the norm, special versions of popular sites are likely to become more common. I don't think we'll need an iPhone, Treo, and Blackbetter versions. But I do think that Web site designers will need to start generating sites, and CSS, that are more flexible for devices with different screen sizes and aspect rations.
Update: Watch Scoble and Gillmor talk about Facebook for the iPhone.