* On the iPhone, you “click” with your fat fingers. Links and buttons may need to be bigger to accomodate this.
* On the iPhone, you have to scroll the page around a lot more than you do on a large desktop screen. Ideally, you design for minimal scrolling on the iPhone.
* On the iPhone, typing is much more painful than on a desktop computer, and you can’t copy/past. Because of this, you may design forms with more select/radio type fields, rather than text input.
* On the iPhone, you don’t have access to Flash or Java bits.
* Etc.

The mobile context (for both the iphone and other mobile devices) has several unique aspects, too.

The point of doing specific designs for iPhone is that we recognize the unique context iPhone users are in when they visit our sites, and we want to give them the best possible experience for that context.

Are iPhone-specific sites necessary? No. The iPhone can browse websites designed for desktop computers in a totally passable way. But, for some of us, “passable” isn’t good enough. The only way to make something that kicks ass on iPhone is to design for iPhone. Period.

dotMobi: http://mtld.mobi
dotMobi (the informal name of mTLD Top Level Domain, Ltd.) was appointed by ICANN as the official global registry for the .mobi top level domain.

dotMobi is backed by leading mobile operators, network device manufacturers and Internet content providers. Our investors include Ericsson, Google, GSM Association, Hutchison, Microsoft, Nokia, Orascom Telecom, Samsung Electronics, Syniverse, T-Mobile, Telefónica Móviles, TIM, Visa and Vodafone.

dotMobi Show cases, try it in your mobile, and you will love it:
google.mobi
msn.mobi
yahoo.mobi
bofa.mobi (Back of America)
Nokia.mobi
AAA.mobi
fox.mobi
foxnews.mobi
quote.mobi
weather.mobi

too much to list here …

@Andrew — I’ve corrected the link.

@Johannes — I fully agree that there is a need for mobile-adapted design, and that it should take precedence over an iPhone-specific design. And in defence of the websites mentioned above, at least Amazon and Facebook already offer good sites for general mobile use (slim and compact pages, mobile-appropriate navigation) — not sure about the others. They’ve already got the general mobile users sorted out and still have cash left to spend, so they go a step further and make the iPhone version as a kind of intermediate between mobile and desktop (still a single-column layout, but with a more fancy design).

The separation of content, design and technology isn’t quite that simple though, due to the huge variation in phone browsers’ capabilities. Some browsers have very restrictive limitations, and these may affect the possible range of content if you don’t want to simply settle for the lowest common denominator. A second point is that navigation needs to be structured differently in a mobile site (in a nutshell, you can’t have as many links in a page as you could have in a desktop site). One day there will be frameworks which allow you to separate all these things cleanly, but I don’t think we’re there yet. At the moment, they really are different versions, merely drawing from the same data sources.

About the second point: I think that Iphone craze is not only about the device but also about the possibilities it offers (like e.g. direct Itunes connection and mobile internet connection via hotspots). Granted, the Iphone IS sexy as a gadget. But comparably to the introduction of the Ipod, people will soon notice that Apple is neither the only nor the best manufacturer of multifunctional bling-bling. Even worse, the Iphone has quickly gained the aura of “really cool, but mindlessly expensive and technically premature” which Apple managed to avert from the starting Ipod years earlier.

So, what will survive from the gigahype? The Iphone as an early adopter’s toy: Interesting right now, but no more than a smartphone among others within a year or two. And, much more important: Mobile services for everyone. Apple clearly was one of the pioneers, bringing the matter to the public. But others will come along with cheaper devices and cheaper rates, allowing the phenomenon to spread.

About the first point from above: Since Safari handles normal web sites, I cannot see a particular need for special *Iphone* web design. But: I see the need for *mobile* web development. (That’s the point where you Ept guys come in.) Which does not mean that web pages will have to be rewritten from scratch - in most cases only graphically redesigned. On the other hand there will arise web services which will only make sense in a mobile web context (like e.g. a bakery locator or tourist information).

So the overall goal must be to strictly separate content, design and technical background (like scripts) of a web site. This way, your informations will be adaptable to perfectly match any interface, be it a computer, a smart phone, a screen reader or your printer. Special versions no, special design yes.