Ok iPhone again – since it sells so well before it’s even shipping.
This handheld computer, with mobile phone capabilities added to it, is as everybody knows by now a flat touch sensitive screen allowing gesture navigation, which comes handy for zooming in and out or scrolling. The device’s only and most important button (except of the sleep button as long as energy is in short supply that is) is the home button. In whatever application you are, this button brings you right back to the initial screen, which displays all applications or widgets you can use on this mobile device.

Now undeniably the finger is a much better pointing device than a stylus, especially since it is quite hard to loose it. The finger has one bad characteristic though: it is covered with skin and skin sweats. Our bodies ‘breathe’ through the skin. The skin regulates our body temperature and it forms and communicates our touch sense not mentioning the shielding of our inside. And since it is doing so much for us, it is undergoing a constant renewal process. And in this process a lot rubs off.

A bit of this rubbing off you were already able to see when Steve Jobs first touched the screen to unlock the device for the then following presentation. That’s natural – no worries – happens to all of us. And it happens even with devices which screens you hardly touch ever – but somehow one always gets these fingerprints on them.

Now it is not the intention to get too annoying by elaborating on what implications there might be if you are presenting a device covered with your fingerprints being a little bit sticky to someone to have a look, but have your swipes (best wet) ready.

What is more interesting is to look at the disappearance of buttons or keys other than the most important one. Apple being rightfully famous for their research and development in user interfaces obviously came to the conclusion that it is essential for the user to have the ultimate assurance in form of a physical button: Press it and we will bring you home – wherever you are!

So why is the home button a physical button? Ever seen a one and a half year old toddler on the loose in your living room? What causes the biggest attraction? Round rubber buttons best in bright colours! Or: TV on – TV off, VCR on – VCR off, HiFi on – HiFi off - best combined with a little beeping sound.

We recognise from a very early age on this form of interaction immediately and because of the on/off nature one learns to understand the particular attached action very quickly.
Down to the technical nature of physical buttons we have the reassurance that it has one particular function and not a multiple set of vague possibilities on offer.

Another very important factor is the felt resistance when we press a physical button. We feel as soon as we have overcome this physical resistance of the button and know instantly when the action is released and we can expect the result.
The transportation of the touch sense is much quicker and the processing of the signal means by far less effort for our central nervous system than for instance if we would trigger a virtual button on screen. There the only possibility is to show the release of a button mainly through visual means i.e. changing of the colour or shadow, a mimicry we need to interpret in our brains first, hence it takes much longer and means more of an effort even if we talk about fractions of milliseconds and tiny amounts of calories we need to burn.

And one must not underestimate the notion of trust if one compares a virtual interface and a physical one. Everyone who has some experience with using a virtual interface has had some disappointments where the interface did not work or the interface reacted in a totally unintended way. An experience usually followed by disappointment mounting to anger or with un-experienced users it raises self-doubt and frustration. And that means stress. So if you can avoid stress – that’s a good thing, isn’t it? Life is too short to get stressed about buttons. With one word – users in general find it more convenient to use physical buttons and the experience is more satisfying.

Which brings us back to the touch sensitive screen of the iPhone. With a little imagination one can see the fantastic possibilities the gesture navigation and handling open up. If it comes to the old fashioned keying in of letters certain doubts remain. The space available for every single key is not necessarily generous (nor is it on most other handheld devices – sliding keyboards on the wider side should not go unnoticed - like HTC efforts) though the visual solution for the feedback when a letter key had been pressed is interesting since it reminds one of the action of an old typewriter which throws the single keys towards the page.

Nevertheless the physical action as on other devices is missing – the praxis will show how satisfying this virtual replacement is. Maybe it would be interesting to look at solutions, which combine the freedom of virtual interface with the aspects of a physical one where polymer layers deliver the haptic qualities on top of the virtual interface elements  – now that would be quite something!