3. Touch Screen: Touch screen mobile phones provide keypad with touch screen technology, which simply means that a keypad will be displayed on the screen and you can use it by touching the keys on the screen. Each touch gives a vibrating response.

      Earlier touch screen phones provided a tactical keypad, which were used as basic keypad. For entering alphabet you had to touch the key specific number of times.Soon most of the touch screen mobile phones started providing QWERTY keypad.

Some touch screen phones also come with handwriting input. For handwriting input you will have to write in a particular fashion for it to get recognized. Touch screen phones are very useful for people who like fast navigation on their phone. Touch screen phones usually have large screens hence consume more power and require frequent charging.

Some mobile phones have combined different keypad types resulting in following types of phones:

1. Touch screen with Tactile keypads: These phones have touch screen facility along with basic keypad. Touch screen provides good navigation and the keypad improves the text input. These phones have small screen and need a stylus or fingernail tip for precise input. Presence of touch screen means power usage of the device is high but not as much as of a complete touch screen phone. To incorporate both touch screen and keypad, size of these phones is larger as compared to a usual “candy bar” or complete touch screen mobiles.

2. Touch screen with QWERTY keypads: These phones provide QWERTY keypads with touch screen. These phones have advantage of both QWERTY keypad and touch screen. QWERTY keypad makes text input very easy and faster where as touch screen makes navigation very simple because you can click wherever you want focus on the screen.

The main consideration is that these phones are very bulky and consume more power, which is similar to mobile phones with touch screen and tactile keypad. The keypad can be kept just below the screen thus reducing the screen size or it can be kept under the screen and can be opened by sliding.

b. Mobile Phone Operating Systems

A smartphone (a high-end mobile phone that offers more advanced computing ability and connectivity) runs a complete mobile operating system. Such operating systems can be installed on many different phone models. They can run third-party applications, using an application programming interface.Widespread examples are:

1.        Apple iOS

2.        Google Android

3.        Microsoft Windows Phone 7

4.        Nokia Symbian

5.        BlackBerry OS

6.         Bada OS