Four Key Principles of Mobile User Experience Design

Prior to becoming a senior UX designer at Popular Front Interactive, I spent two years as a mobile UX researcher within the Georgia Institute of Technology’s Mobile Technologies Group – a lab tasked with both future-casting and then rapidly prototyping innovative mobile experiences.

As I transitioned from academia to industry, I discovered that while mobile UX was discussed, it wasn’t discussed from the same broad frame of reference that I was used to within the confines of a research-based institution. Although more recent mobile UX conversations I have found myself in have undoubtedly benefited from the ongoing smart phone revolution, overall I still find these conversations to be needlessly driven by tactical adoration and lacking a conscious consensus regarding the fundamental principles of the mobile-user experience.

I do not presume these following principles to be all-inclusive or ultimately authoritative; rather, it is my hope that they are received as an anecdotal summation of my findings that might then spark and contribute to the larger conversation and consensus-building process.


PRINCIPLE #1: There is an intimate relationship between a user and their mobile device.

While an intimate relationship between an individual and their mobile device may seem like a given, the depth of that relationship probably goes deeper than most initially realize. In fact, I argue that the relationship extends to a physical level and the exchange of bodily fluids.

Imagine that it is a hot summer day and someone asks if they may borrow your mobile device to make a call. You hand it over. What level of trust does this simple act portray? Consider those around you right now: How many of them would you loan your mobile device to without hesitation? In your social circles, is it acceptable to decline such a request? How does context influence this scenario? What if you are at work? At a bar? How about a family reunion?

Let’s assume that this person is noticeably respectful of your device and the personal data it contains while making their call. At the call’s completion, the individual immediately and graciously returns it, whereupon you notice that it has accumulated an amount of … goo (perspiration, humidity, etc.) that is typical of mobile device use on a hot, sticky summer day…but then again, it isn’t your goo.

From a gooey physical level to a level of data privacy and security, there is an intimate bond between an individual and their mobile device, the strength of which often elevates the mobile device to the status of iconic personification. I am my phone. My phone is I.

In order to meet user expectations, mobile experiences should assume a semi-guarded state of primary usership; however, we must also responsibly protect our users. As the trend of embedding ourselves into our mobile devices increases, so does the cost of our devices being compromised. Assume primary ownership, allow for secondary usership, and plan for what might happen should we lose ourselves.

In a worst-case scenario, a compromised mobile device containing a significant amount of personal data would become the networked equivalent of a voodoo doll, where actions performed via the mobile device could cause actual harm to the individual personified by the device. In cases such as this, a remote wiping of all data on the device may be a user’s only recourse. 


PRINCIPLE #2: Screen size implies a user’s state. The user’s state infers their commitment to what is on the screen.

Imagine that you have been looking forward to seeing a particular blockbuster movie since the day it was green lit, and now that the day of its release has finally come you are going to get the most out of the experience by going to see the movie on the largest IMAX screen in the tri-state area.

Let’s say that when you finally take your seat in the sold-out theatre, you notice the person sitting next to you has a very annoying laugh. There is nowhere else to sit in the theatre, and you’ve been dying to see this movie for more than a year. What are the chances you abandon the experience and walk out? Probably fairly slim to none.

Now let’s say that you were backpacking through Europe when the above blockbuster was released, and that you have been equally anticipating the movie’s Blu-Ray release. To celebrate the release, you and your friends are gathering at the home of the friend who has an impressive home theater featuring a 52-inch HD screen, and again you find yourself seated next to the guy with the annoying laugh. Now how likely are you to abandon the experience? Probably more so than above, but still not likely.

What if this scenario played out in a college dorm room and the movie was being viewed on a 22-inch computer monitor? What if you were sitting next to the guy with the annoying laugh? The chances that you might abandon the experience are probably increasing.

What about a mobile device’s 3.5-inch screen? Is there any way you would sit next to some random person with an annoying laugh for 90 minutes to watch that movie? Probably not.

Although there are any number of social and environmental factors that would affect the user abandonment rate in the experiences described above, it is consistently possible to estimate a user’s level of commitment to an experience based upon the size of the screen through which they are engaging it.

Since mobile devices are likely to be the smallest screens in a user’s experience, the design of mobile experiences must accommodate the user’s varying commitment and distributed attention. How an experience accommodates these conditions will change depending on experience type — game, banking application, or the like — but the underlying impetus remains the same.


PRINCIPLE #3: Mobile interfaces are truncated. Other interfaces are not.

A dreaded task that usually accompanies getting a new mobile device is the act of transferring your data from the old device to the new. In years past, this meant arduously re-entering all of your contacts via the device’s, most likely E.161 (12 key), keypad.

There were a few early, notable attempts to ease this burden. GSM service providers pushed device manufacturers to save all user data to the devices SIM card by default, but the card’s limited storage capacity produced a poor user experience. On the other hand, CDMA service providers began automatically transferring address books between devices as a customer service. Even early on it was widely acknowledged that although an individual wanted to use information on their mobile device, they would go to great lengths to avoid having to manually enter that information.

Palm, and later Research in Motion, sought to improve this fact of mobile user experience by introducing and then proliferating the practice of syncing. This concept paired the truncated mobile interface with a full-sized desktop interface, allowing the user to easily and reasonably efficiently enter their address book data via a familiar QUERTY keyboard. Although this feature was initially limited to smart phones, it has since been incorporated into a wide swatch of consumer-grade devices. In fact, the notion of syncing has become so ubiquitous in mobile computing that the syncing of one’s entire networked identity is a core plank of Google’s Android operating system.

Even as miniaturized QUERTY became and becomes a more standard feature for all mobile devices, the truth remains that mobile interfaces are truncated and better used for manipulating data rather than entering it. One might conclude that as mobile devices continue to incorporate increasingly impressive sensor arrays, even standard, consumer-grade devices will provide powerful data collection capabilities. Regardless, data collection is not data entry, and data entry is not likely to become a mobile-appropriate activity. 


PRINCIPLE #4: Design for mobile platforms — the real ones.

There is a prevailing tendency is to discuss mobile platforms in terms of device manufacturers and service providers. This is understandable. It is fun and easy to get caught up in the moment of the latest tech demo, press release, or rumor. However, in needlessly binding the dialogue to the news of the day, we create unnecessary segmentation across an already complex landscape. The overall conversation is better served by focusing on the mobile platforms that have emerged as constants over time. Those four platforms are voice, messaging, the internet, and applications.



Voice was the original mobile platform, but it is also the platform with the most nebulous future. Don’t get me wrong: People will always need to make an occasional phone call. However, the frequency with which we are doing so is declining. Why? Mobility is as much about efficiency as anything else, and telephony (vocal communication and vocal response interfaces) has proven more difficult to optimize compared to other methods of interactivity.

For example, let’s say that you wanted to verify that your paycheck had been deposited. Most banks offer both tele-banking and online account access. Which interface are you likely to use, and why? How about if you wanted to order a pizza? Would you rather call, be placed on hold for five minutes, and then dictate your order to a multi-tasking teenager, or would you rather just use a GUI to do it?



Friedhelm Hillebrand, the architect of the messaging (SMS) specification, described the platform’s limit of 160 characters as “perfectly sufficient.” The question we must ask ourselves in considering this mobile platform is, “Perfectly sufficient for what?” Although Hillebrand can provide several reasons for how he arrived at the 160-character limit, the one that I have always found the most interesting is that his team discovered that most postcards typically contain 150 characters or fewer.

Have you received or sent any postcards recently? If you have, they were likely either brief social communications (“Having a great time. Wish you were here!”) or they were simply task-oriented such as RSVP-ing for a wedding or canceling a subscription.

Messaging trends today continue to affirm Hillebrand’s postcard comparison. The vast majority of SMS traffic consists of social interactions within small groups of individuals. The second tier of usage is comprised of simple task-based transactions such as voting, entering contests, and receiving notifications.

In both cases, SMS and postcards, content-heavy experiences are a minority occurrence as the media is not designed to accommodate such a level of engagement. Furthermore one could argue that due to the designed efficiency of the messaging platform, that a content-heavy experience would be far from appropriate. 


The Internet

The Internet is the most awkward of the mobile platforms in that it is the one that is the least natively mobile. Currently almost 95% of all Internet users experience the web via displays with resolutions of 1024×768 or greater. As such, 1024×768 is observed as a fairly universal standard and is what a significant portion of Internet-based experiences are designed to. Given that mobile displays typically range between resolutions of 60×120 and 480×320, it is fairly obvious that most Internet-based experiences aren’t designed with mobile users as a primary consideration.

As a means of making Internet-based experiences more accessible to mobile users, most mobile web browsers have been designed to include adaptive methodologies for displaying larger experiences on smaller screens. While these adaptive tactics, which typically employ pan and zoom-esque interactions, have undoubtedly made more of the Internet accessible to mobile user, one could hardly argue that it has resulted in a desirable user experience. In fact, if browsing the Internet from a desktop is regarded as a scanning activity, than browsing the Internet through the adaptive lens of a mobile browser might best be described as a squinting activity.

As mobile web usage has continued to emerge as a somewhat common activity, the assumption that Internet-based experiences are to be automatically adapted for mobile users has given way to the design of alternative experiences specifically for mobile users. While this trend has provided mobile users with more efficient and scannable web experiences, it also has the potential of overplaying the users’ expectations for Internet-based mobile experiences.

As Internet-based mobile experiences have become more device-centric and sophisticated, they have begun to resemble mobile applications, thus creating a scenario where users might expect the Internet-based experience to function as a mobile application would. The distinction between desktop applications and Internet-based experiences may be rapidly evaporating, but it remains germane in the mobile experience. Although there are several differences between the platforms, the primary point of contrast I will draw here is that applications are able to use device-level services such as sensors, ad-hoc networking, and optics, whereas Internet-based experiences cannot. While mobile browsers are beginning to make some of these services available to Internet-based experiences, each platform will always have affordances the other doesn’t. As such, and to manage user expectations, if an experience looks like an application and attempts to behave as an application would, then it should be an application — and vice-versa.



From a technical standpoint, applications represent executables that are native to a specific mobile environment, have been selectively installed, and have access to the device’s full array of available functionality. However from a UX standpoint, they represent a specialized interaction design that caters to an affluent, sophisticated, and targeted mobile user base.

As few as 24 months ago, the seemingly basic task of locating and installing an application on a mobile device required a fairly developed skill set. With the recent proliferation of “app stores,” this task has become more user friendly; however the percentage of users who are able to install an application on their mobile device nowhere near approaches that of those who know how to make a phone call or send a text message. So, regardless of recent improvements to the overall process of acquiring and installing a mobile application, the user who can perform this task would still be considered sophisticated compared to the overall segment.

All things considered, mobile applications might best be described as the boutique mobile platform. As is the case with most boutique experiences, a comparatively small audience will compensate for itself through fervor and zealotry. However, since the success of an application-based mobile experience is based almost entirely upon acceptance within that small audience, extraordinary attention must be paid to the particulars of the target audience’s needs and behaviors. What existing need is the application attempting to mobilize? What efficiencies can a focused interface bring to that workflow? How can the specific affordances of a mobile device augment and improve upon that experience in contrast to using one of the other mobile platforms?

Mobile applications are powerful tools…for a relatively small segment of individuals who want them and know how to use them.



Someone tweeting on behalf of Punchcut once wrote, “In mobile UX, don’t confuse precedence with standard.” I couldn’t agree more, but as I hope that I’ve successfully illustrated, this statement is well ahead of where the conversation should be. Both standards and precedence are both tactical perspectives. Within our context, they both represent distinct libraries of interactions and are either redefined as the landscape evolves or simply replaced as more elegant solutions are brought to market.

The variable nature of each of these categorizations only further demonstrates why it is best for the current mobile UX conversation to focus on higher-level principles rather than tactical particulars.

As mobile UX designers, we have both opportunity and choice in front of us. The opportunity is to establish the foundation principles of a stable, yet still emerging, experiential space. The choice lies between getting caught up in the excitement of the fad du jour or asking ourselves the difficult question of what foundational principles am I following, or establishing, with the work that I am currently doing.

The only unfortunate part is that the time we have to make this decision is quickly running out.


  1. Principle #2: I don’t think you mean “infers.” I think you means “conveys” or “indicates.” “To infer” is to read something and to “get something out of it,” or to pick up the meaning that is “implied” but unstated. I wouldn’t normally point out issues of grammar, but in this case, I really had a hard time understanding what this principle was intending to convey.

  2. On further reflection, I think you mean: “A user’s commitment to using the interface is only as great as the device’s screen size.” In other words, as screen size increases, so does the user’s commitment to using the application, and the same is true in reverse. I’m not sure that “state” is helpful in conveying this principle. Better to stick with simple English.

  3. Thanks for the comment R.

    I used “infer” intentionally in the sense that one can reasonably deduce/estimate a user’s commitment to an experience based upon their screen size. As I have found that this principle is not without it’s exceptions, I wanted to stay away from the terms you suggested which might present the concept as more of a presumed universal associative property which would not have been my intent.

  4. Dakota,

    “mobile applications might best be described as the boutique mobile platform.”

    Thanks for the insightful article. It is a good reminder that while many folks have a whole slew of apps loaded on their phone, their is a user difference in those that have and have not installed applications.

    It would be great to see a more open format for sharing apps across the board. Also, I think application packs that offer a bundle of well used and trusted apps would improve the download/install experience. Not just the mobile world, but lots of software suffer this exact problem in the form of plugins, modules, updates, and add-ons. Each seem to have their own spin on the solution, but it has increasingly become an apparent design problem without a standard solution.


  5. Re your predictions on Voice – that it has a ‘nebulous’ future: I think that speech is the easiest, lowest effort, fastest means of communications for humans, and that will not change. What will change is the ability of machines to do speech recognition, so your scenario of calling a multi-tasking teen for a pizza order will actually become you calling 1-800 GOOG-411, asking for pizza, and then ordering the type of pizza you want by talking to a machine. What becomes interesting, and difficult, is the development of multi-modal, including touch and voice input, interfaces for mobile devices. Voice is not going away.

  6. Thank you for the Article, but I am left with many questions.

    To begin, how are we defining mobile devices. Do we include “dumb” cell phones. Is the Kindle a mobile device? a PSP? A digital camera? This is relevant when discussing a truncated experience and the platform.

    If mobile devices offer a truncated interface, which platform are we discussing and truncated compared to what? How is the interface for mobile voice communications truncated?
    I’m also not clear on the distinction between data entry and data collection.

    When discussing applications, why do we distinguish between applications installed by the user and ones that come included with the device? And I would argue the line between Internet and application is irrelevant.

    I enjoyed the article but it does not align with what I see on the subway every day.

  7. @Phil

    I wholeheartedly agree that voice will never go away. My rationale for labeling it’s future as nebulous pertains to the challenges of designing experiences that utilize vocal input. On a high level those challenges map to social concerns of public vs. private communication and the inefficiency of vocal input.

    First the social implications… How many places is it socially appropriate for you to carry on a private conversation in public? That’s what vocal input equates to- an audible private conversation between you and your device. There are places where this is acceptable and appropriate (while driving in your car), and there are places where this is a social no-no (in a crowded elevator). There are also places where this could end your career (during a meeting). The personal nature of the mobile space privileges discreet interactions, and often, speaking out loud is often not discreet.

    The second challenge I see is, as I said, is the general inefficiency of vocal interface compared to GUIs. In your case study, since I don’t have that number on speed dial, it would be 12-13 keystrokes before I even had the opportunity to start to place my order. In addition to this, vocal-only interfaces have difficult time confirming user input since the only option that is typically available is ‘reading the order back’ to the user.

    If we consider your vocal/GUI combo, then we arrive at the model employed by most fast food drive-thrus where you say your order out loud and receive visual confirmation of the order via a display. My question to you is, would you still use the drive-thru if you were able to simply key in your order ahead of time (potentially paying for it in the process) and then just pick it up at the window.

  8. @Richard

    Very good questions here. Let me see if I can answer them.

    As far as how are we defining mobile devices, I don’t necessarily have a strict definition for that but I think that all of your examples would qualify. As we work towards a definition I we need to look at which platforms a device supports and whether or not those platforms are opened or closed.

    “Dumb” cell phones have open support for voice, sometimes messaging, and sometimes the Internet while offering typically closed support for applications. The Kindle offers closed support for applications, and arguable closed support for the Internet as well. While the PSP offers closed support for applications and open support for the Internet. Finally a digital camera typically just allows closed support for image recording applications.

    Moving on, my colleagues and I typically joke that an interface is truncated as long as you wouldn’t want to use it to write your thesis with. To use another example I can access relatively the same Internet with my iPhone as I can on my laptop, but I’m not likely to use my iPhone to do research for an article. I can type that article on my my 12 inch laptop, but I would much prefer to do so via the full sized keyboard that resides on my desk.

    I agree with you that voice isn’t necessarily truncated, as it is the most native of the mobile platforms, but it has similar problems with efficiency.

    As far as data entry vs. data collection: Data entry would be manually typing in a 50 character URL into your mobile device’s web browser. Data collection would be scanning a QR Code that contains that URL and having the associated webpage open automatically in your browser.

    Why do we distinguish between pre-installed apps vs. user installed? The most simple reason is that it demonstrates user segmentation. It is one thing to know how to use the app that controls your mobile devices camera, it is another thing all-together to be the kind of user who knows how to install an alternative app with camera-control functionality.

    Finally the most basic point I can make to demonstrate relevancy of the line between the Internet and applications is that using the Internet on a mobile device requires an active data connection while this dependency doesn’t necessarily exist for an application.

Comments are closed.