In the last few years, user interfaces on smart phones have undergone a sort of renaissance. What was once a stylus driven experience reminiscent of a desktop PC, has now become a finger friendly endeavor that offers new design paradigms. The iPhone is largely responsible for driving this change by showing people a phone can be easy to use with a capacitive touchsceen. The big players in the space area all working to provide the best user interface in their own way. Now that we've seen Android 2.2, iPhone OS 4.0, and even some early builds of Windows Phone 7, it's possible to see where user interface is going. 

Let's go over some of the bigger milestones in phone UI design and see what they mean for the future of phones.
 

Know your roots

Not that long ago, most smartphones felt like using small, sluggish PCs. Sure, at the time we thought we were pretty cool toting around our Windows Mobile phones, oblivious that there might be a better way to use a phone. Most methods of interaction in this era relied on having a stylus. UI elements were often small and tucked in corners of the screen. There were also scrollbars aplenty. A stylus is actually a very precise method of interaction when paired with a resistive screen. 

One thing these earlier smartphones understood is the idea of having information easily accessible. Windows Mobile provided a way to run rudimentary widgets (of course we didn't call them that) on the home screen. It was simple to check out weather or your upcoming appointments without actually launching an application.  

RIM was also a player in the early days of the smartphone and brought some useful user interface conventions. The Blackberry has not traditionally relied on any sort of touchscreen display, but rather on a trackball. The Blackberry was aimed almost exclusively at business users at first, so speed was of the essence. The user interface did a good job of making things easily accessible. With just the trackball, functions were no more than a few clicks away. Unfortunately, the Balckberry UI hasn't evolved much since then, and the straight porting of the Blackberry OS to touch devices like the Storm felt ham-handed.
 

The iPhone changes the tone

Until now, touchscreen have been useful in some situations, but no one really wanted to use them as the sole means of controlling a phone if they could avoid it. People wanted buttons and physical keyboards. It would take a man that hates buttons to move smartphone interfaces ahead. When Apple introduced the iPhone, with just a single button that had any effect on the UI, people were skeptical. But little by little the benefits of using a finger on a capacitive touchscreen to control the phone became more apparent. 

Overall, the precision of a capacitive touch screen is not as high as that of a resistive screen. So the idea of cramming lots of controls and menus on the screen was a no-go. Everything need to get a little bigger, and move further apart. This is the basic premise of being "finger-friendly". The iPhone strives to remain as easy to use as possible. This is due in part to the home screen interface. nearly the whole interface is an app launcher. Most of the phone's functions are accessible right there. The home button can be used to bring up a few additional controls (I.e. the iPod or the quick launch bar in OS4), but most of the action happens on the screen.  

The use of capacitive touch also allowed for the use of interface elements like multitouch. Apple may not have invented the idea, but they were the first to make it useful on a mobile phone. We feel like predicating a user interface on having a capacitive touchscreen makes sense. And Google apparently agrees with us.
 

Android borrows some, invents more

Android, which was launched about a year after the iPhone, takes that idea an runs with it. Phone running Google's mobile OS also rely on capacitive touchscreen, but the interface is a more free experience. If a user so chooses, an Android home screen can be utilized just like an iPhone with row upon row of app shortcuts. Though, a pull up menu has the full list of apps. When you tap on one of these shortcuts to launch it, the app fills the screen with a slick animation. 

Returning to the home screen is accomplished with the Home button. This is fairly common in phone user interfaces these days, but Android has something else to bring to the table. Android also uses the idea of the long-press as a substitute for a right-click on a PC. This means fewer UI elements need to be displayed on the screen as they are accessible via long-press only when needed. Long-pressing the home button offers up a list of recent applications as well. We've always been taken with the way the Android UI handles notifications. Unlike the iPhone where they interrupt your use of the phone, Android tucks them away in the status bar. Sliding it down displays your notifications in a really slick way.
 
Android includes a full featured widget framework to extend the user interface. This allows users to have access to information without opening up a new application. This may come at the expense of simplicity, but many enjoy the benefits of widgets. The widget is just a graphical front end that accesses data and can display it to the user as part of the larger interface. This is contrary to the iPhone model that requires an app to be lunched to obtain any information.
 

The Palm strategy

Palm's WebOS was a sort of gambit to combine the usefulness of the Android multitasking ability, with the simplicity of the iPhone. For the most part, it turned out to be successful in doing so. The home screen interface on WebOS is a playground for the so-called "cards" that represent each program. When running an app, users can easily jump back to the home screen. But unlike on a computer, the program doesn't hide itself anywhere. Instead it exists as a card that can be brought back up or closed. Multiple cards can line up horizontally to be selected from. 

Palms first year of WebOS was a rough one that ended with the company being sold to HP. Part of the issue may have been some sluggishness exhibited by WebOS, which was commented on in most reviews. Palm tried a clever user interface trick to alleviate some user frustration. Now when opening an app, instead of the phone only displaying content when it's done loading, it will show an empty card and a glowing icon. It's just a subconscious trick that makes the phone feel faster. Behold the power of clever UI design.

The future

We thought we'd see everything smartphone user interface design had to offer, but when Microsoft showed off Windows Phone 7, we found out we were wrong. It shouldn't come as a surprise, it's not like we saw the iPhone coming either. Windows Phone 7 drops the traditional home screen UI completely. It works on a system of "Hubs" for common functions. The Hubs act as both shortcuts and as a widget of sort that can display pictures or data from within the Hub. Users can scroll vertically to see all their hubs and they can be reordered. 

Content within the Hubs is ordered in a fashion that has the user scrolling horizontally to see all of it. if you've used a Zune HD, you're familiar with the idea. For example, when selecting the People Hub, users are first presented with recent contacts, scrolling to the side will offer the entire contact list.
  The new iPhone OS has been previewed and is also looking to shake things up. Most of the interface looks the same, but they've added a new user interface for limited multitasking. Double clicking the home button will bring up a list of recent apps. This is similar to the Android launcher, which is accessed from a long-press of the home button. Adding this to the iPhone means less bouncing back to the home screen. App states are saved, but they don't actually run in the background. We feel it will make for a more streamlined user interface. There's also support for folders to help clean up that app list. 
 
Android's moves right now are all about polish. Froyo (2.2) isn't a dramatic departure from 2.1, but it does a lot to make the interface more usable. How? Well, by making it faster to navigate. The Android interface sometimes feels a little inconsistent, and getting around can take too long. One solution is the addition of phone and browser shortcuts that sit at the bottom of the home screen with the launcher. This means no more bouncing back to the home screen to start the browser, or place a call. But having the system respond more quickly (which Froyo does) goes a long way to improving the user experience as well. Google is also looking to get your information more integrated. Contacts have Facebook and Twitter data connected to them, and the photos you see in various apps are linked to all the data you have on that contact. This is a design paradigm we find useful, and it's nice to see Google expanding it.

User interfaces will continue to change as more capable hardware and aster data networks become available. We have no way of knowing what the next iPhone-like UI advancement will be, but we probably won't see it coming. In the coming years, we believe the big challenge will be keeping the mobile UI innovative, without becoming overly complex. Even now, there are times that Android can end up a little too smart for its own good. The use of multitasking is also becoming more pervasive, and we'd like to see a better system for doing it. Palm's method is attractive and easy, but limited. Ideally, a hybrid of Android's background processes and Palm's intuitive interface should happen. Wherever things go, we'll enjoy the ride. Let us know what you consider to be the most important user interface design paradigms in mobile.