Body The size of the phone in format (H x L x W) and the volume of the phone where available. If the phone has a flip, it is measured with the flip closed.
Display There are lot of display types used in mobile phones. They can be either color or monochrome. Monochrome displays on the other hand can be alphanumeric or graphic. Alphanumeric displays can show only symbols with a constant size, while graphic displays can show fonts of different sizes and animations.
The color displays usually are CSTN, TFT, TFD or OLED with a predominant use of TFT displays in current mobile lineups. There are also two types of touchscreen displays - capacitive and resistive, which are both based on TFT technology.
CAPACITIVE touchscreens work by sensing the electrical properties of the human body, while RESISTIVE ones operate by sensing direct pressure applied by the user.
Camera Some phones feature a camera that gives them the ability to work as a digital camera. Often (though not always) the camera is also able to shoot video.
The most important characteristics of a camera are the resolution (measured in megapixels), lens focus type (either fixed or automatic) and the presence of a flash. The flash could be either LED (single or even double) or xenon.
The number of megapixels is not always a good measurement of the quality of the photos, but if you plan to print pictures, you would generally get higher quality ones out of higher megapixel cameras.
Auto focus lens are not a guarantee of better image quality, but fixed focus cameras are usually inferior. Most importantly, only auto focus cameras can allow shooting of really close objects - i.e. macro shooting.
Some phones offer optical zoom but those are rare. Most use digital zoom, which degrades the quality of the photo.
Cameras that can work in "video mode" are characterized by the maximum resolution and framerate (frames per second or fps) of the recorded video.
Sound The mobile phone can alert you of events such as an incoming call or an incoming message in a number of ways. The two most popular ones are vibration and ringing.
While vibration is pretty much self-explanatory, the ringing alerts can be of several types depending on the mobile phone.
In the past mobile phones used to allow only monophonic tones to be set as ringing alerts. With the advancement of technology, polyphonic ringtones also became supported.
Later on as mobile phones further evolved, they started using MP3 tones for various alert purposes. As more (presumably superior) audio formats became available (such as AAC), they were also added to the mobile phones' alert system.
Recently, mobile phones have even started to use short video clips as call alerts (not to be confused with video calls).
Features Modern mobile phones come with a variety of sensors that automate or easy many of our daily tasks. This field takes into account the presence of an accelerometer, a gyroscope, a compass, and a barometer.