There is no agreement in the industry about what a smartphone actually is and definitions have changed over time.[6] According to David Wood, EVP at Symbian, "Smart phones differ from ordinary mobile phones in two fundamental ways: how they are built and what they can do."[7] Other definitions put different stresses on these two factors.

Most devices considered smartphones today use an identifiable operating system, often with the ability to add applications (e.g. for enhanced data processing, connectivity or entertainment) - in contrast to regular phones which only support sandboxed applications (like Java games)

In terms of features, most smartphones support full featured email capabilities with the functionality of a complete personal organizer. Other functionality might include an additional interface such as a miniature QWERTY keyboard, a touch screen or a D-pad, a built-in camera, contact management, an accelerometer, built-in navigation hardware and software, the ability to read business documents in a variety of formats such as PDF and Microsoft Office, media software for playing music, browsing photos and viewing video clips, internet browsers or even just secure access to company mail, such as is provided by a BlackBerry.

The first smartphone was called Simon designed by IBM in 1992 and shown as a concept product that year at COMDEX, the computer industry trade show held in Las Vegas, Nevada. It was released to the public in 1993 and sold by BellSouth. Besides being a mobile phone, it also contained a calendar, address book, world clock, calculator, note pad, e-mail, send and receive fax, and games. It had no physical buttons to dial with. Instead customers used a touch-screen to select phone numbers with a finger or create facsimiles and memos with an optional stylus. Text was entered with a unique on-screen "predictive" keyboard. By today's standards, the Simon would be a fairly low-end smartphone. The Nokia Communicator line was the first of Nokia's smartphones starting with the Nokia 9000, released in 1996. This distinctive palmtop computer style smartphone was the result of a collaborative effort of an early successful and expensive PDA model by Hewlett Packard combined with Nokia's bestselling phone around that time and early prototype models had the two devices fixed via a hinge; the Nokia 9210 as the first color screen Communicator model which was the first true smartphone with an open operating system; the 9500 Communicator that was also Nokia's first cameraphone Communicator and Nokia's first WiFi phone; the 9300 Communicator was the third dimensional shift into a smaller form factor; and the latest E90 Communicator includes GPS. The Nokia Communicator model is remarkable also having been the most expensive phone model sold by a major brand for almost the full lifespan of the model series, easily 20% and sometimes 40% more expensive than the next most expensive smartphone by any major manufacturer.