What is a mobile phone?

This is just a brain-storming exercise really. A mobile phone isn't just a mobile phone, it's lots of things. These things are listed here. This is a high-level "features" list, some are provided by pure software (such as an address book) and some by hardware, usually driven by some software.

So, a mobile phone is/maybe a(n)...

Regular Phone!
No, really it is! A phone has the ability to make voice calls to other phones using the Plain Old Telephone System (POTS). More information about hardware which provides POTS functionality can be found in the Main_Page section.

VoIP Phone
If the phone has access to the internet, or some other IP-network it has the possibility of becoming a VoIP phone.

Video Phone
If the phone has a camera attached to it, it can make outgoing video calls. This may be using a 3G standard or provided by an IP video phone solution. Even if it doesn't have a camera, you could still see the other person if they have a camera.

"Headless" Phone
If the phone isn't being dialed by a human, or being talked into by one, it can generate its own audio for a voice call, or just use the cellular link as an internet access mechanism for some automated TCP/IP client or server application.

Instant Messenger
Be it SMS messages, MSN messager or ICQ, most phones have the ability to send & recieve short text messages (sometimes with a photo/video clip/audio clip). Perhaps a Jabber Client.

Clock
Often overlooked, but many people use their phone to work out what time it is. There's other things you can do with this, like a stopwatch, a countdown timer or an alarm. Perhaps Alarms could be integrated into a calender? If connected to a GPS, an ultra-accurate clock could be set.

Video Player
Play video stored on your phone, or perhaps a bluetooth HDD. You could also have a Digital Terestrial TV decoder and use your phone as a TV. There's also user-generated online content such as google video or YouTube.

Mapping Device
Many GSM modules also have a GPS module built in, which could be used to show the user where they are. Even if it doesn't have GPS, it could still have a mapping application on it. Online content could also be integrated with the map using standard geo-location APIs & RSS feeds. E.g. Traffic reports for your area, wifi-coverage overlays, pizza huts, blog entries. If your on holiday, read someone else's comments on a temple your about to go and look round.

Personal Information Manager
Applications such as a list of contacts. The phone number can be called using the "Regular Phone" functionality. The address could be fed into mapping functionality to navigate you to their house. Lots of other possibilities also exist such as a calender, Todo list, etc.

Camera/Camcorder
A device which takes still photos or perhaps a clip of video. It might be possible to include the location the photo was taken at if a GPS is connected. Better still, the angle & direction the photo was taken, provided by an electronic compass & accelerometer. Why not then upload the photo you've just taken to Flickr or a video to YouTube?

News reader
Usenet or RSS reader, the latest news delivered directly to your pocket.

Encyclopedia
Either a shortcut to Wikipedia for your web browser or a complete off-line digital encyclopedia (perhaps derived from the Wikipedia CD project).

Web Browser
Either a WAP browser or even better, a fully fledged, flash-capable web browser.

Games Console
From Pong to Quake 3, all have been ported to mobile devices.

File Storage Device
Why carry round a USB-pen stick if your phone's got a few GB of storage space? Maybe you'd like to send a file to someone else using bluetooth or IrDA?

Torch/Flashlight
Dropped your keys? Or perhaps your Ice Climbing in Scotland and find the batteries have died in your headtorch and need to top-out by phone-light? 

TV Remote Control
If a phone's got IR, perhaps it could be used to change channels on you TV? LIRC might be a way to go here.