General-purpose touch-screen devices have delighted users since the HP-150 debuted in the early 1980s. Today, three years after the iPhone's introduction, nearly all "smart" mobile telephones have touch screens and their interfaces force interaction almost exclusively through this means.
Which is great unless the user is a fat-fingered, myopic palsy victim.
I upgraded from a Moto RAZR v3 to an LG Xenon (AT&T) this year. I wanted the keyboard because I am fat-fingered, myopic, and now thanks to middle age, presbyopic (TANJ!). Despite the tiny keyboard, the interface seems to demand I use the touch screen to accomplish most tasks.
My daughter taunts, "Daddy, you're such a slow texter."
"Bite me, kid. I'm a QWERTY touch typist and T9 sucks at 1337."
The crux of the problem is this: the touch screen doesn't feel me. The screen's touch points, despite training, are inaccurate or unresponsive. Forget typing via touch screen using 'ABC' or T9 mode. Sometimes I jab it several times to get it to read once.
The reason is my fingertips are callused, their skin dry. If I lick the tip of my pinkie and use that finger, it works great. Of necessity I've personalized the phone with my own slobber. Ew.
For whom are these touch interfaces designed? Tiny, moist-fingered kogyaru? Racoons?
The Real Problem
Humans vary widely in size and physiology, as do the environmental conditions under which they work. Interfaces must work under these conditions, too, or offer clear workarounds when they cannot.
Vendors of course put the cheapest interface device into the phones because phones are disposable commodities. My LG Xenon cost nothing on promotion so long as I signed up for another two year tour of duty aboard the Death Star Phone Company.
The Getting Started guide that ships with the AT&T-branded LG Xenon is a thick pamphlet with little info. The 146-page version of the full manual, once hunted down online, offers a list of features matched to buttons and screen symbols, but no help for sending a text message when the on-screen send touchpoint won't react. After a hour's fiddling it turns out that pressing the SEND key (labelled with a green telephone handset icon) steps through the SMS select destination and transmit message sequence.
Happily, the HANGUP key (labelled with a red handset symbol) is the go back in sequence key. Except when it isn't.
Fixing the Design
Designers must consider more than happy path operation when the device offers multiple physical interfaces. By comparison, Microsoft does multiple interface paths well enough. They code and document keyboard shortcuts that make Windows fully usable without a mouse.
Test interfaces with various pointing device types, widths, and surfaces. Fingers may be wide or slender, wet, dry, greasy, sticky, dirty, bloody, or damaged and misshapen. Styli may be fingernails, real nails, pens, pencils, pencil erasers, screwdrivers, paper clips, dowels, coffee stirrers, and so forth.
Try operating them under common, real-world environmental conditions. Range from humid to dry and include insult conditions such as heat, cold, drizzle or rain, soda pop and coffee spills, oil, grease (skin lotion or sunblock), and paint (fingernail polish). Is the phone usable after Junior scribbles over the touchscreen with a Sharpie?
What is the workaround if the touchscreen fails to react altogether? For many applications, the phone is now bricked. Not so bad if a replacement is available, but potentially lethal in an emergency situation, say, after an automobile crash.
Document not just the feature set and the normal way of operating, but also the alternate, non-touchscreen method for getting work done. It's only paper.
And please, ship the real manual with the product. At least print the URL on the box.