An infrequent series of gadget blogging posts ...
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There's an argument going on on the internet right now about the merits of larger screen sizes on smartphones. Proponents argue that gizmos like the new Samsung Galaxy S II (with a 109.22mm screen diagonal) are somehow better than the iPhone 4S (with its wearyingly 2009-vintage 88.9mm screen) purely because of the bigger screen.
Interestingly, the food fight has moved on from absolute number of pixels on screen — with 800 x 480 pixels on the Galaxy SII versus the iPhone's eye-bleeding 960 x 640, most adults can't see any sign of the jaggies when holding their phone at arm's length.
Rather, this fight is all about ergonomics ... and the iPhone boosters are wrong this time.
The proponents of the iPhone size screen point out that, holding the phone in one hand, with a 3.5 inch/90mm screen you can reach all the icons on the screen with your thumb; whereas around 40-50% of the screen real estate is out of reach on the larger phones. The larger screen actually makes the phone more cumbersome and less useful as a phone. Bigger screens, they argue, are like tail fins on 50's automobiles, and if the vendors want to make them functional they need to invest design chops in a user interface that allows one-handed use.
pushers proponents of the bigger screens point out (rightly) that the iPhone's 90mm screen is visually cramped and a 110mm screen is nicer to look at.
I'm going to side with the big screen folks this time; while those who accuse them of being badly designed for one-handed use are absolutely correct, they're wrong about the shape of the overall argument.
They're wrong because a smartphone is not a dumb phone.
The use case for a dumb phone goes back to the old rotary dial land line phone; you have a control dial to input the number you're calling, then a handset with a microphone and speaker that you hold to your head while you talk. Let me emphasize that: while you talk. Phones were all about talking.
Then we got dumb cellphones and could talk without the wire. So the functionality of the base station (bells and dials and switches) was merged into the bit you held to talk into. They acquired numeric keypads.
Circa the early 1990s, GSM phones began to turn up. They included some neat features — wireless data, and the ability to send control messages up to 160 characters long (originally developed for pagers, now generalized to all over the air systems). People rapidly began to use text messages for their own purposes.
Fast forward a few years, through the early smartphones (yes, I owned a Treo 600) to the modern touchscreen smartphones.
Our current generation of smartphones are not optimized for talking to people. You can use them as a dumb cellphone, but frankly, the call quality is usually horrible because what they're really designed around is communications. This may involve SMS messaging, or its multimedia sibling MMS, or voice calls over the telephone network, but it probably involves internet usage: email, instant messaging, web, IP telephony via Skype or similar, stuff like Apple's Facetime — internet video telephony.
(In the past month I've made maybe half a dozen voice calls. In that time, I've sent many tens of text messages, and sent and received numerous emails, on my iPhone.)
You do not cram a videophone against the side of your ear. Ditto an email terminal. You hold it in front of your face. Probably in both hands, because thumb-typing with two thumbs is faster than thumb-typing with one hand.
That's the first argument for larger screens on smartphones; they're text terminals and text input works best with two hands (at least, unless Siri exceeds expectations — which I don't expect it to in the short term, because as I understand it it needs to be internet connected all the time in order to work, and our current networks aren't fit for purpose).
The second argument is based on eyeballs.
Most of our global civilization has, or is about to, undergo a phenomenon called the demographic transition. A side-effect of the DT is that the age profile of the population skews towards the elderly. From early middle age on, your eyeballs lose acuity and in particular the lenses in your eyes become less able to focus on nearby objects — presbyopia (or "long-sightedness") cuts in. In most of Western Europe the average age is now around 35-40; in Japan it's higher. This is the age profile of the 21st century.
Anecdote time: I had a little accident on my flight to the 100 Year Starship conference. It was a long-haul, and I took my glasses off to get some sleep for a couple of hours. I woke up needing the rest room as one does on a 9 hour flight, stood up ... and managed to rip the arm off my varifocals (which were partially nested in a niche on the back of the chair in front). So I was forced to resort to my emergency spare glasses, ones adapted to the vision of a 40 year old.
I have an iPhone 4 and am generally happy with it. But during my couple of weeks without decent visual correction, I have found myself holding the iPhone at arm's length in order to focus on it — at which distance it's not emitting quite enough light to be easy to read. The ultra sharp display hovers just slightly out of comfortable focusing distance. Web browsing became unaccountably fatiguing. And I got a brutal reminder as to why I still carry a Kindle ebook reader when I fired up the Kindle app on the iPhone.
It is no fun to have to take your glasses off whenever you want to look at your iPhone, or to squint at it from arm's reach. This, for me, is one of the key weaknesses of the iPhone/iPod Touch form factor. The user interface is very pretty, but it has been designed for twenty-somethings, or for adults with high quality visual correction. If your visual correction is just slightly off, or you have other eye trouble, the small smartphone form factor is a disaster waiting to happen — especially if it's your main computing device (as it probably will be, in years to come).
I mentioned earlier that the smartphone is a text terminal. This isn't necessarily true for all users or all time — it's just my personal bias. I found Facetime surprisingly useful for keeping in touch with my wife on my long trip in July/August; as higher data rate networks like LTE roll out, I expect multi-way video calling to really take off. There are other high bandwidth visual things folks do with these devices. Things for which having a large, clear screen will be more important than the ability to reach all the controls one-handed. Like, oh, reading ebooks or watching movies comfortably.
The iPhone 4S looks nice, but when I bought my current phone I planned to wait until it was at least 24 months old before replacing it, and I've seen nothing to change my mind so far. The one feature that Apple could add that would cause me to whip out my wallet right now would be a 110mm (or larger) screen with the same pixel count as the current 90mm screen, and ideally a keyboard optimized for two-thumb typing (like the one iOS 5 is set to bring to the iPad later this week).
TL;DR: it's not about one-handed phone use; folks who think in terms of smartphones as a one-handed device are still stuck in the telephone age). The real bone of contention is what to do about ageing eyeballs in the era of visual media. While the market for one-handed talk-to-me gadgets is declining, the number of folks with sub-optimal eyesight is only going to grow with time. It doesn't matter how much more convenient it is to use a gadget one-handed, if you can't see the screen. And we're trying to display so much information via smartphones that something has to give: my money is on the screen diagonal.
There is a wild card in all this, and that wild card is Siri — intelligent voice-controlled navigation. If it can really be made to work, we may be about to see the smartphone market fission completely — into screenless intelligent assistants that clip to your ear like a bluetooth headset, and compact tablets for those of us who want to thumb-type with both hands. But we're still in the early days of cloud-mediated conversational AI assistants ...
 Both in terms of data service availability and in terms of what happens the first time you get off a plane in a foreign country and get sideswiped by $9.50/megabyte international roaming charges.
 If you wear glasses or contacts all the time, you should always pack an emergency spare set in your luggage when you travel. Even if it's just the old pair you replaced in daily use a couple of years ago; partial visual correction is still way better than none at all. Ditto any essential medication: trying to find an emergency doctor in a country where you don't speak the language really sucks.
 I turn 47 next week. It's downhill all the way ...
 You can have readable text on screen but have to turn pages every ten seconds, or you can have a pages' worth of text on screen and need a magnifying glass to read it. Or you can use an e-reader with a 150mm screen diagonal.