It's generally useful to have an agreed-upon definition for what an industry does. So, what is the wireless industry? What is a mobile? Does it have to be a phone? What about a Blackberry or Sidekick?

Lets start with the devices. A Blackberry is definitely in. An iPod is definitely out. It doesn't have connectivity and isn't used for communications. What is the difference?

The wireless industry is focused on communications. I propose we refer to the set of related devices as Personal Communications Devices, or PCDs. These are epitomized by mobile phones and text communications devices like the Blackberry.

A PCD is:

• Personal. The device generally belongs to only one person, and is personally identifiable via messaging address and ongoing service.
• Communicative. The device sends and receives messages and connects with the network in a variety of ways.
• Handheld. The device can operated with a single hand, even if two hands or a hand and a surface are more convenient.
• Wakable. The device can be awakened at a single touch by either the user or the network. A mobile phone will receive a text message even when in its “sleep”, or standby state. Note that most computers, if they are asleep, can not communicate with the network.

This combination of features conspires to make the service indispensable and the PCD an ever present part of the user's life. The service represents safety and social connection. Because the service is indispensable, users tend to carry the device with them all the time. This fact forms the core of understanding mobile user experience.

The fundamental distinction between mobile-targeted design and design targeted for other platforms is The Carry Principle: the user typically carries the device, all the time.