Last November I was invited to Sweden to participate in the annual Conference on Mobile and Ubiquitous Multimedia, MUM2003. It gave me the opportunity to meet a number of people in that industry, and to learn about the cutting edge of mobile game design. While I was there I collected a series of observations about mobile games that I thought I would share with you.

"Mobile" is really too broad a definition to be useful. In principle it includes everything from Tamagotchi to console machines built into airplane seats. In practice "mobile" seems to have come to mean "networked handheld." A handheld device without communication capabilities is still perfectly mobile, but the Game Boy Advance seems to be excluded from the category of mobile game machines, because it can't transmit to other mobile game machines. Many people think mobile games specifically means games played on cellular telephones rather than handheld game devices even if they are networked. When talking about mobile games, it's important to be clear exactly what platform you mean, because the differences among them are so great.

Currently there's a huge tug-of-war between personal digital assistants (PDAs) and cell phones. As manufacturers add more features to each, their functions are beginning to overlap, especially in storing name and address data. Until recently cell phones were getting smaller and smaller, and had gotten down to about the size of a candy bar, but as they have begun to compete with PDAs, they're swelling back up again.

Looking at the forms of these devices, it seems to me that a PDA needs a minimum screen size in order to be useful as a handheld computer. A PDA exists to serve the eye. The primary requirement of a PDA is that you be able to hold it in one hand and write on it with another. For this reason a phone makes a poor PDA. (Blackberry-style keyboards are just barely acceptable, in my opinion--I prefer to carry a separate fold-up keyboard if I need to use one with my PDA, so that I can touch-type with it.)

	The various GameBoy devices do only one thing--play games--but do it very well.

A phone, on the other hand, exists to serve the ear. Its primary requirement is that you be able to hold it up to your ear and talk to it, without nearby people being able to hear what the other side is saying. (We don't mind people hearing one-half of our conversations, but we insist that they obtain a wiretap warrant if they want to listen to both halves.) A PDA makes an awkward, barely acceptable phone.

A gaming device such as the Game Boy Advance serves the eye and the ear together, but its primary design consideration is to serve the hand. Handheld game devices must be comfortable to hold and manipulate for long periods of time. They need large, conveniently placed buttons and joysticks. Neither phones nor PDAs offer convenient input devices; phones in particular seem to be getting more awkward rather than less, as manufacturers implement oddball layouts for the sake of styling. Nokia's recent circular dial may be visually reminiscent of rotary phones, but why?

The Nokia N-Gage is suffering commercially because it falls between two stools: the game device and the mobile phone. It's too small and awkward to be a convenient handheld game system. It's too big to be a convenient mobile phone. It weighs too much and costs too much. And if that weren't enough, you have to take out the batteries to change the cartridge.

	Nokia's N-Gage is an interestering hybrid between phone and portable game device.

In the West, PDAs are an adults-only device; game handhelds are a children-only device; phones are devices for everybody. Therefore we will see the broadest range of game types for mobile phones. (Handhelds are gaining acceptance among adults, but I have yet to see an adult playing with a Game Boy on the train.) Children are a natural target market for mobile games because they move around a lot and have a fair amount of leisure time. With adults the situation is not so straightforward. People will play mobile games in intervals between doing other tasks, which suggests that their games actually should be simpler and shorter than those for children!

I don't foresee women playing a lot of online mobile games. Sexist though it may sound, I think if a woman is going to pay for airtime, she'd probably rather spend her money talking or sending messages to a friend than playing an online game. This isn't universal of course; millions of women will play online games…but I think women will play them less often and for less time than men will. This may change with 3G, "always-on" phones, however.

I would expect Europe and the Far East to be much larger markets for mobile games (proportionally to their population) than the USA for one simple reason. In Europe and Asia people take the train and subway to work, whereas (except in the larger cities) most Americans drive to work. For Americans, commuting is not downtime but drive-time, and that means they can't play games.

There are a lot of different ways to slice up the domain of mobile games: by platform, online or offline, and so on. Another of these distinctions is between games that are "essentially mobile" and those that are "incidentally mobile." Essentially mobile games are those in which mobility is a part of their gameplay. "Incidentally mobile" games are those that can be played equally well on stationary platforms.

There aren't, at the moment, many essentially mobile games. There have been a few experiments, but not much more. During the Experimental Gameplay Workshop at the Game Developers' Conference last year, Steffen Walz presented a game called M.A.D. Countdown in which participants ran around a building with networked handheld computers trying to find a "bomb." In 2001, an art group called Blast Theory, together with various other institutions, created a game called Can You See Me Now? that involved real players running around in a real city (Sheffield, England and Rotterdam, Holland were among those used) trying to catch imaginary people being controlled over the Internet by others. Both of these events demonstrated some of the potential of essentially mobile gaming, but also some of its weaknesses. In Can You See Me Now, players ran a real risk of stepping in front of a car because they were concentrating too hard on their mobile equipment, which they carried to tell them where the imaginary players were. In addition, the batteries tended to run down, and it was often difficult for the runners to get a fix with the Global Positioning System in the cluttered urban environment.

I think the number of people who want to play essentially mobile games--and above all, to pay for the privilege--is going to remain small, perhaps on the order of the number of people who play paintball or laser tag. Given the choice of running around outdoors with a handheld computer or sitting indoors playing video games (with convenient access to a bathroom and a refrigerator!) most people would surely choose the latter. The greatest potential for essentially mobile games, it seems to me, is not in games designed for use anywhere, but in those designed for particular locations. Theme parks, nature parks, zoos, and museums are enclosed, safe spaces where people can move freely without having to worry about traffic. We've had handheld audio guides for years; it would be a simple matter to make them interactive and then to turn them into games.

	The PalmOS-based Zodiac aims to combine the best of PDAs and mobile game devices.

Despite all the hysteria about predatory behavior on the Internet, anonymity--when properly used--makes the Internet a very safe place. It's just a question of teaching children to be on guard, and setting appropriate boundaries for them.

However, a phone or other device that enables one stranger to track the position of another in real space has great potential to be used by predators--especially if children are involved. Essentially mobile games that permit this will need some mechanism for restricting the players of any given game to a known, approved group.

Another design consideration for essentially mobile games is in the scale of the play area. If the game is scaled for walkers, it may be possible to cheat by using a bicycle or a car. If a game is scaled for cars, then it must necessarily be spread over several miles.

Mobile games have a great future, but for the time being nobody really knows what that future is. Just as the circumstances of play are quite different between the PC and the console (monitor versus TV; mouse versus controller, etc.), so the circumstances of play are different between mobile and fixed devices. Those circumstances will have a powerful influence on their design.