The form factor of a mobile phone is a general description of its shape and mechanical function, and can have a big impact on the usability of the cellphone.
The most basic shape is the candybar which is at least as long as a Mars Bar, almost as thick and somewhat wider. This provides space for a small screen and a numeric keypad, while keeping the manufacturing costs low by avoiding any moving parts. Examples: Nokia 1208, Motorola F3.
A variation is the slate or tablet form factor. This is wider than the candybar, and much thinner. It allows for a larger screen and an alphanumeric (Qwerty) keyboard. Examples: Nokia E71, BlackBerry Curve.
A fold on the shorter dimension makes a flip phone, which provides several advantages. It greatly increases the length, enabling the microphone to be placed much closer to the user’s mouth, yielding increased call quality. It also enables the very natural “open to answer” function, which is much more convenient than scrabbling around to find a button to press. And when it’s folded up, accidental button presses are impossible. On the downside, no functionality is available when the device is folded, unless additional buttons and a duplicate display are provided on the outside (which defeats the benefit of no accidental button presses inside your pocket). Examples: Motorola RAZR, BlackBerry Flip 8220.
To achieve increased length without the need for a second display, the slider form factor can be used. This puts the display on the face, with a numeric keypad sliding out from underneath when making a call. Examples: Samsung J700, Nokia N82.
If the slide goes sideways, it can expose a full alphanumeric keyboard. The side-slider is popular with those who send lots of text (SMS) messages, and with those who do lots of mobile web browsing. Examples: LG KS360, Nokia N97.
By folding away an alphanumeric keypad rather than sliding it, we get the clamshell shape, like a tiny version of a laptop computer. Examples: Nokia 9300, Nokia E90.
Unusual and uncommon form factors include the swivel (Samsung F210), detachable keyboard, dual slider (up/down, or sideways/down), dual-flip (vertical/horizontal) and dual-fold (left and right, Nokia 6810). But manufacturers always want to keep the total volume down, and the more complicated the mechanism, the less space remains for the electronics.
One way to reduce the mechanics even further is to do away with a conventional keyboard, making the screen do double-duty as a touchscreen keyboard. This works really well for web browsing over a cellular connection or playing touch-enabled games, but can be less convenient at other times. Examples: Apple iPhone, LG Viewty II.
Cellphones can also be made as wristwatches, incorporated into a headsets, surrounded by rubber to ruggedise them, or made into novelty shapes. There’s also a market for outrageously-priced bling phones, encrusted with diamonds or pearls.
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