Michael Gartenberg Michael Gartenberg has covered the personal technology beat for more than two decades at places like Gartner, Jupiter Research and Altimeter Group. Most recently, he spent a few years at Apple as Sr. Director of Worldwide Product Marketing.

There was a time when mobile devices were easy to classify. Phones were for talking, cameras were for taking pictures, and media players were for listening to music. The smartphone changed that, and iPhone brought it to the mass market.

With the rise of the smartphone, it would appear any question of consumer preference to carry a single device vs. multiple standalone devices has been settled. After all, it's hard to find a category, from photos to games, from maps to music, that a modern "phone" can't do. Today's phones indeed do it all. They're multitaskers par excellence. So, does that mean there's no market for uni-taskers?

I'm not so sure. People will carry more than just a phone if their needs dictate, but that doesn't mean people will carry more than they need to. Past data I've seen suggests there's an upper limit to how many gadgets will make the cut at any one time. That leads me to what I call the "mobile rule of three." People prefer to carry one device but will carry up to three if necessary.

Context is the key

While it appears there's a contradiction in terms of what consumers will carry and what they prefer to carry, I don't believe the two are at odds with one another. Many consumers will own and carry multiple devices based on context, always tending to carry the fewest devices possible at any given time. They simply want to carry as few as are needed, and don't want to carry more than three.

iPhone, for example, makes a great Swiss Army knife for so-called "everyday carry". If you're going on a long plane ride or are spending the day at the beach, perhaps a Kindle might come in handy. Taking your first trip to Italy or going on that long-planned safari, considering bringing a camera with an assortment of lenses. Going on a run or skiing the hills, perhaps an iPod may still make sense.

I believe mobile devices are following two trajectories: Multitaskers gain more and better functions, becoming "good enough" to fill many needs, and uni-taskers mature and gain even greater capabilities. Sometimes it's not enough, like the withering mobile gaming console market once dominated by Nintendo. Other times it is, like the digital camera market.

The uni-tasker is dead, long live the uni-tasker

I don't think the uni-tasker is dead. I think some of them will fade from relevance but others will still have a place for a while to come. I do think that if you're a vendor in the device space, it's time to think about where you fit into the hierarchy of the consumer mobile ecosystem.

People will carry more than just a phone if their needs dictate. They just won't carry many more. That's the key for vendors to understand. In a world where the "rule of three" is real, you can't be device number four.