Unless you do design for something totally unambiguous like mobile phone OSs, you might has "what do you mean by mobile?" And the answer is, well, kind of a broad range of things, and not a very quick answer.

While other portable devices pre-date modern mobile telephony (both the Gameboy and the GPS network are earlier than GSM), mobile phones have evolved fastest, absorbed other technologies and form a useful core technology to consider all others. The evolution of mobile can be considered as:

1. Voice
2. Paging and Text
3. Pervasive network connectivity
4. General computing devices

If you consider a current mobile phone as a generally 4th era device instead, what you find is they are:

• Small - Enough to be carried around essentially all the time ETC.
• Portable - Battery powered AND ALL THAT IMPLIES...
• Connected - Wirelessly. Not attached to the wall, and connected in multiple ways, to both voice and data networks.
• Interactive - Inherently. Unlike a watch, or even most MP3 players, which are limited to display, playback and a small subset of interactions.

If we use this definition, then pretty much all mobile phones are included.

And some other devices in the "MID" (mobile internet device) range, such as the iPod Touch and the recent spate of mobile tablets. So, "mobile" is also:

• Things very like mobile phones, but without the mobile radio,
• and things very like mobile phones, but with different form factors.

But what if you are one of those folks who glues an iPad to down, to make it an ad hoc kiosk? It's no longer small, it's not portable anymore, so what is it?

Well, obviously it's a mobile device still. And if so, then the gut feeling is that so are GPS receivers, portable game systems, maybe even TV game systems, and that why not DVRs, and so on.

But certainly not TV video programming, and not my itronix, explain why...

So...

• Contextually-aware
• Highly-interactive
• Constrained interface

...Constrained interface might seem to be a problem, but really it's not. if you put a real, full-size keyboard on a mobile device, the keyboard acts like a desktop computer, and suddenly all text input follows desktop computing patterns, not mobile patterns... this works!

..........

More interestingly, if you start losing individual definitions, even more comes into play. GPS devices are only a bit unconnected; some have full network, some have FM traffic reports. But why draw a bright line between them based on connectivity, if all other factors are the same, and you design them the same way?

• So, I also might add sensors. Laptops are just portable desktops. A laptop with full desktop software, but radios, and accelerometers and GPS is... arguable. And will be more muddled over time.

This leads to definitions more related to "small screen" and "interactive." It lets even embedded devices (printers), media-capture (camera) and playback (mp3) devices play. And actually looking at the patterns, the vast majority apply to all these device.

I think if you consider the convergence chart (not originally from, but visible at http://shoobe01.blogspot.com/2010/10/f8-and-be-there-what-mobile-convergence.html), and consider what happens to all those converged devices, interesting things occur. Now, what if you take out the backbone, and let there be MIDs (iTouch, etc.) that do everything but telephony? Might be good as an anchor to build the argument from, or another axis of argument. Plus, nice image.

OTHER THOUGHTS:

This needs work. Some of us think it's all small screen devices. Connected or not.

Connectivity away from the wall is another definition. But kills many game devices. And actually, GPS, and so on, since they are receiving only.

Restrictive interactions also seems valid. At least as an edge case; why can't the same patterns be applied very often to say the LCD on your photo-printing inkjet?

Need to define this. What's your opinion?

What Patterns Do You Cover?

Good question. And right now, it's purposefully muddled. We don't generally talk about hardware, except for labels and key functions and and keyboard layouts. Because those are pretty easy to change, and directly impact the on-screen interactions. Though we /could/ talk about how people with gloves, or dry fingers, or who just hate touchscreens should also have a scroll-and-select keys, at least as backup. But, that's pretty high level handset design, so not really worth fighting in a book like this.

So, the definition is pretty much on-screen, and things that directly impact the on-screen experience that are plausible to consider changing, for at least an operator/carrier to change, even if not everyone can.

If you have the ability to influence hardware design, then you can still get some hints from the patterns and principles contained here. We also, likewise, make lots of references to complying with the principles of the OS, as well as having principles that may conflict with any particular OS. So, if you design operating systems, then you have some other patterns and principles and guidelines to work off as well.