Way way after the first telephone and not-so-way before VoIP phones, there came devices that tried to continue the first phone's purpose (to provide instant communication across long distances) and added some features that did not exist before (wireless communication). They are smaller than the ordinary landlines and some have antenna(e), obvious or not obvious. They are called mobile phones, precisely because of their use in mobile communication.
Most of these phones connect with each other through a series of cellular sites (a cellular network or a base station). Because of this, mobile phones also came to be known as cell phones. Note however that some mobile phones do not connect to cell sites. Example of these are satellite phones.
Originally, mobile phones are meant to be used like landlines but without the cords attached to them. As technology progresses, however, additional features that were ordinarily seen in other devices were also incorporated with these phones. Some of these are short message services (SMS) used for text messaging, polyphonic tones, 'real' tones (they are actually .wav and .mp3 files stored in the cell phone), imaging, videos, GPRS (General Packet Radio Service; used in mobile Internet), 3G, and, more recently, mobile television. And they were incorporated in just a short span of time.
With the rate new mobile phone technology is moving, is it not exciting to wait for the 'next big thing'? Who knows, next time we might even see a full-length movie playing in our phones. Now THAT is something to look out for. Can't wait for that.
In the end, however, despite all of the fancy stuff that the new models come up with, mobile phones' most important features are those that were already made out a long long time ago--during the time when the mobile phone's father is invented. That is the ability of the mobile phone's to let you talk and communicate with anyone around the globe.